Organic electric field light emitting element and production therefor

ABSTRACT

A composition for an organic electroluminescent device is a composition for forming an organic light emitting layer of an organic electroluminescent device by wet coating process. The composition contains a phosphorescent material, a charge transport material, and a solvent, in which the phosphorescent material and the charge transport material are each an unpolymerized organic compound, and the first oxidation potential of the phosphorescent material E D   + , the first reduction potential of the phosphorescent material E D   − , the first oxidation potential of the charge transporting material E T   + , and the first reduction potential of the charge transporting material E T   −  satisfy the following condition: 
         E   T   − +0.1 ≦E   D   −   &lt;E   T   +   ≦E   D   + −0.1 or  E   D   − +0.1 ≦E   T   −   &lt;E   D   +   ≦E   T   + −0.1.

FIELD OF THE INVENTION

The present invention relates to a composition for an organicelectroluminescent device which can easily yield an organicelectroluminescent device through wet coating process, and the resultingorganic electroluminescent device has an excellent luminous efficiencyand a satisfactory operating life. It also relates to a thin film for anorganic electroluminescent device, a transfer member for a thin film foran organic electroluminescent device, and an organic electroluminescentdevice, each of which is formed by using the composition for an organicelectroluminescent device. In addition, it relates to a method ofmanufacturing the organic electroluminescent device.

BACKGROUND OF THE INVENTION

There have been developed electroluminescent devices using organic thinfilms (organic electroluminescent devices). Materials for organicelectroluminescent devices can be roughly classified into low molecularweight materials and high molecular weight materials.

There have been developed organic electroluminescent devices using lowmolecular weight materials. Examples of such devices include an organicelectroluminescent device having a hole transport layer formed from anaromatic diamine, and a light emitting layer formed from aluminum8-hydroxyquinoline complex; and an organic electroluminescent deviceusing aluminum 8-hydroxyquinoline complex as a host material, doped witha fluorescent dye for laser, such as coumarin. Low molecular weightmaterials such as the following platinum complex and iridium complex arealso used as materials for light emitting layers.

There have also been developed organic electroluminescent devices usinghigh molecular weight materials such as poly(p-phenylenevinylene)s,poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]s, andpoly(3-alkylthiophene)s; and devices using high molecular weightmaterials such as polyvinylcarbazoles, in combination with low molecularweight luminescent materials and electron transfer materials. Most ofsuch devices using high molecular weight materials are manufactured bywet coating process such as spin coating or an ink jet process, inconsideration of properties of the materials.

Focusing attention on processes for forming thin films, films of mostlow molecular weight materials have been formed by vacuum deposition,and films of most high molecular weight materials have been formed bywet coating process. The vacuum deposition is advantageous typically inthat a film with good quality can be uniformly formed on a substrate,that a multilayer film can be easily formed to yield a device havingexcellent properties easily, and that contamination of impuritiesderived from the manufacturing process is very little. Accordingly, mostof organic electroluminescent devices currently used in practice areformed by vacuum deposition using low molecular weight materials.

In contrast, the wet coating process is advantageous typically in thatno vacuum process is required, that a film with a larger area can beeasily obtained, and that one layer (coating composition) can containplural materials having different functions. The wet coating process,however, has following problems, and most devices formed by wet coatingprocess are not developed to a practical level, except for those usingsome high molecular weight materials.

It is difficult to control the degrees of polymerization and themolecular weight distributions of high molecular weight materials(polymerized organic compounds).

When devices are operated continuously, terminal residues causedeterioration of the devices.

It is difficult to purify high molecular weight materials highly, andthe resulting materials may contain impurities.

As an attempt to solve these problems, following Patent Document 1 andPatent Document 2 each disclose the use of low molecular weightmaterials (unpolymerized organic compounds) each containing afluorescent substance, a hole transport material, and an electrontransport material, instead of high molecular weight materials(polymerized organic compounds). This attempt is intended to reduce thedrive voltage by allowing the hole transport material and the electrontransport material to transport holes and electrons injected from ananode and a cathode, respectively. The resulting devices, however,operate at high drive voltages and have insufficient luminousefficiencies, because holes and electrons are not sufficiently injectedfrom the anode and cathode, respectively. Oxadiazole derivatives used asthe electron transport material are insufficient in drive stability(operation stability) and thereby insufficient in operating life. Inaddition, it is difficult to adopt a phosphorescent material or ablue-emitting material as a luminescent material, because the resultingluminescent material has a large energy gap.

-   Patent Document 1: Japanese Patent No. 3069139-   Patent Document 2: Japanese Unexamined Patent Application    Publication No. 11-273859

DISCLOSURE OF INVENTION

An object of the present invention is to provide an organicelectroluminescent device which has an organic light emitting layerformed by wet coating process, enables charges to be injected fromelectrodes into the organic light emitting layer satisfactorily, andshows an excellent luminous efficiency and a satisfactory operatinglife.

According to a first aspect of the present invention, there is provideda composition for an organic electroluminescent device, including aphosphorescent material, a charge transport material, and a solvent.Each of the phosphorescent material and the charge transport material isindependently an unpolymerized organic compound.

In the composition, the first oxidation potential of the phosphorescentmaterial E_(D) ⁺,

the first reduction potential of the phosphorescent material E_(D) ⁻,

the first oxidation potential of the charge transporting material E_(T)⁺, and

the first reduction potential of the charge transporting material E_(T)⁻

satisfy the following condition:

E _(T) ⁻+0.1≦E _(D) ⁻ <E _(T) ⁺ ≦E _(D) ⁺−0.1

or

E _(D) ⁻+0.1≦E _(T) ⁻ <E _(D) ⁺ ≦E _(T) ⁺−0.1

According to a second aspect, there is provided a thin film for anorganic electroluminescent device, which is a thin film formed from thecomposition for an organic electroluminescent device according to thefirst aspect through wet coating process.

According to a third aspect, there is provided a transfer member for athin film for an organic electroluminescent device, which includes abase material and a thin film arranged on the base material, in whichthe thin film is formed from the composition for an organicelectroluminescent device according to the first aspect through wetfilm-formation.

According to a fourth aspect, there is provided an organicelectroluminescent device including a substrate bearing an anode, acathode, and an organic light emitting layer arranged between the twoelectrodes, in which the organic light emitting layer is a layer formedby using the transfer member for a thin film for an organicelectroluminescent device according to the third aspect.

According to a fifth aspect, there is provided an organicelectroluminescent device including a substrate bearing an anode, acathode, and an organic light emitting layer arranged between the twoelectrodes, in which the organic light emitting layer is a layer formedfrom the composition for an organic electroluminescent device accordingto the first aspect through wet film-formation.

According to a six aspect, there is provided a method of manufacturingan organic electroluminescent device including a substrate bearing ananode, a cathode, and an organic light emitting layer arranged betweenthe two electrodes. The method includes the step of forming the organiclight emitting layer by wet film-formation using the composition for anorganic electroluminescent device according to the first aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating an embodiment ofa transfer member for a thin film for an organic electroluminescentdevice.

FIG. 2 is a schematic cross-sectional view illustrating an embodiment ofan organic electroluminescent device.

FIG. 3 is a schematic cross-sectional view illustrating anotherembodiment of the organic electroluminescent device.

FIG. 4 is a schematic cross-sectional view illustrating yet anotherembodiment of the organic electroluminescent device.

FIG. 5 is a schematic cross-sectional view illustrating anotherembodiment of the organic electroluminescent device.

FIG. 6 is a schematic cross-sectional view illustrating anotherembodiment of the organic electroluminescent device.

FIG. 7 is a schematic cross-sectional view illustrating anotherembodiment of the organic electroluminescent device.

FIG. 8 is a graph showing an electroluminescence spectrum of a deviceprepared according to Example 1.

DETAILED DESCRIPTION

A composition for an organic electroluminescent device according to thepresent invention has a long pot life, excellent heat resistance, and alow viscosity, and is satisfactorily homogenous. In addition, thethickness of a film of the composition upon film-formation can be easilyadjusted. By using the composition for an organic electroluminescentdevice, an organic electroluminescent device can be easily obtainedthrough wet film-formation, and the resulting device enables charges tobe satisfactorily injected from electrodes into an organic lightemitting layer and has an excellent luminous efficiency and asatisfactory operating life.

Known organic electroluminescent devices prepared through wetfilm-formation fail to enable charges to be satisfactorily injected fromelectrodes into an organic light emitting layer. They also operate athigh drive voltages and have insufficient luminous efficiencies,unsatisfactory drive stability and operating lives. In addition, theyhave such energy gaps in their luminescent materials as to inhibitpractical use of such devices. In contrast, the composition for anorganic electroluminescent device according to the present inventionsolves these problems in related art. The reason for this has not yetbeen clarified but is supposed as follows.

It has been considered that wide-gap charge transporting materials (hostmaterials) are required for light emission of wide-gap devices typicallyincluding phosphorescent materials and blue-emitting materials. Aphosphorescent material and a charge transporting material can besignificantly involved in injection of either one of hole and electron,and as a result the device can be driven at low voltage, when:

the first oxidation potential of the phosphorescent material E_(D) ⁺,

the first reduction potential of the phosphorescent material E_(D) ⁻,

the first oxidation potential of the charge transporting material E_(T)⁺, and

the first reduction potential of the charge transporting material E_(T)⁻

satisfy the following condition:

E _(T) ⁻+0.1≦E _(D) ⁻ <E _(T) ⁺ ≦E _(D) ⁺−0.1

or

E _(D) ⁻+0.1≦E _(T) ⁻ <E _(D) ⁺ ≦E _(T) ⁺−0.1

When one of the charges (hole or electron) is trapped by the highestoccupied molecular orbital (HOMO) or lowest unoccupied molecular orbital(LUMO) of the phosphorescent material, the phosphorescent material hasan increased lowest unoccupied molecular orbital (LUMO) or a decreasedhighest occupied molecular orbital (HOMO) to such a level as to easilyreceive a charge from the lowest unoccupied molecular orbital (LUMO) orthe highest occupied molecular orbital (HOMO) of the charge transportingmaterial. Thus, the phosphorescent material can emit light with a highefficiency.

When materials satisfy the above-mentioned condition, satisfactoryadvantages are obtained in an organic electroluminescent device having alight emitting layer formed through wet coating process. When the lightemitting layer is formed by vapor deposition, there is generally nodifference between a device which satisfies the condition and a devicewhich does not.

A thin film for an organic electroluminescent device according to thepresent invention is formed from the composition for an organicelectroluminescent device according to the present invention through wetcoating process. The thin film has excellent light-emitting properties,good quality, and excellent heat resistance and is resistant todeterioration even when being electrified over a long time.

A transfer member for a thin film for an organic electroluminescentdevice according to the present invention includes a base material and athin film formed on the base material through wet coating process usingthe composition for an organic electroluminescent device according tothe present invention. By using the transfer member, an organic thinfilm can be easily and conveniently obtained, and the organic thin filmhas excellent light-emitting properties, good quality, and excellentheat resistance and is resistant to deterioration even when beingelectrified over a long time.

An organic electroluminescent device according to the present inventionincludes an organic light emitting layer formed through wet coatingprocess using the composition for an organic electroluminescent deviceaccording to the present invention. A method for manufacturing theorganic electroluminescent device according to the present inventionmanufactures the organic electroluminescent device by forming an organiclight emitting layer formed through wet coating process using thecomposition for an organic electroluminescent device according to thepresent invention. According to the organic electroluminescent deviceand the manufacturing method thereof, an organic electroluminescentdevice having high practicality can be easily manufactured through easyand convenient steps.

Accordingly, organic electroluminescent devices according to the presentinvention can supposedly be applied to flat panel displays such as thosefor office automation (OA) computers and those as wall-hangingtelevisions; onboard display devices; displays for cellular phones;light sources utilizing the characteristics as flat light-emittingdevices, such as light sources for copying machines and backlightsources for liquid crystal displays or meters; indication panels; andmarker lamps.

Some embodiments of the present invention will be illustrated in detailbelow. It should be noted, however, that following description oncomponents is illustrated only as examples (representative examples) ofembodiments according to the present invention, and they are notlimitative at all unless departing from the scope and spirit of thepresent invention.

[Composition for Organic Electroluminescent Device]

A composition for an organic electroluminescent device according to thepresent invention includes a phosphorescent material, a chargetransporting material, and a solvent. Each of the phosphorescentmaterial and the charge transporting material is independently anunpolymerized organic compound.

The first oxidation potential of the phosphorescent material E_(D) ⁺,

the first reduction potential of the phosphorescent material E_(D) ⁻,

the first oxidation potential of the charge transporting material E_(T)⁺, and

the first reduction potential of the charge transporting material E_(T)⁻

satisfy the following condition:

E _(T) ⁻+0.1≦E _(D) ⁻ <E _(T) ⁺ ≦E _(D) ⁺−0.1

or

E _(D) ⁻+0.1≦E _(T) ⁻ <E _(D) ⁺ ≦E _(T) ⁺−0.1

The terms “unpolymerized organic compound”, “phosphorescent material”,and “charge transporting material” herein are defined as follows.

Unpolymerized Organic Compound

The term “unpolymerized organic compound” as used herein refers to anorganic compound other than a compound generally called polymer(polymerized organic compound). Namely, it refers to a substance otherthan a substance containing a high molecular weight polymer or acondensation product formed as a result of chain-like repetitions of thesame or similar reactions of a low molecular weight compound. Morespecifically, it refers to a compound which has a substantially singlemolecular weight and differs from a high molecular weight organiccompound formed as a result of regular or random polymerization of oneor more polymerizable monomers, oligomers, or polymers, according to anyprocess. The “unpolymerized organic compound” has a molecular structurethat can be uniquely and quantitatively defined by a chemical formula.

Phosphorescent Material

The term “phosphorescent material” as used herein refers to a componentwhich mainly acts to emit light and corresponds to a dopant component inan organic electroluminescent device according to the present invention.A component or material is defined as the luminescent material whengenerally 10% to 100%, preferably 20% to 100%, more preferably 50% to100%, and most preferably 80% to 100% of light (unit: cd/m²) emittedfrom the organic electroluminescent device is identified to be from thecomponent or material.

However, the phosphorescent material may have charge transportingability, as long as its light emitting function is not impaired. Thephosphorescent material may include one compound alone or two or moredifferent compounds in arbitrary combinations and proportions.

Hereinafter the “phosphorescent material” is also simply referred as“luminescent material”.

Charge Transport Material

The term “charge transport material” refers to a material that cantransfer a given charge (namely, electron or hole). The chargetransporting material is not specifically limited, as long as it satisfythis condition, and can include any materials. Each of these chargetransporting materials can be used alone or used in arbitrarycombinations and proportions.

Methods of Measuring Oxidation Potentials and Reduction Potentials

The first oxidation potential and the first reduction potential can bedetermined according to the following electrochemical measurement(cyclic voltammetry). A supporting electrolyte, a solvent, andelectrodes for use in the measurement are not limited to those describedbelow, and any supporting electrolyte, solvent, and electrodes will do,as long as a similar measurement can be conducted.

Initially, a tested material (a luminescent material or charge transportmaterial relating to the present invention) is dissolved in an organicsolvent containing about 0.1 mol/L of a supporting electrolyte such astetrabutylammonium perchlorate or tetrabutylammoniumhexafluorophosphate, to yield about 0.1 to 2 mM solution. After removingoxygen from the solution by procedures such as bubbling of dry nitrogen,degassing under reduced pressure, or application of ultrasound, thesolution in an electrically neutral state is subjected to electrolyticoxidation (or reduction) using a working electrode such as a glassycarbon electrode, and a counter electrode such as a platinum electrodeat a sweep rate of 100 mV/sec. The potential of a first peak detected inelectrolytic oxidation (or reduction) is compared with theoxidation/reduction potential of a reference material such as ferrocene,to thereby determine the oxidation (or reduction) potential of thetested material. The oxidation (or reduction) potential thus determinedis further converted into a value versus saturated calomel electrode(SCE) as the reference electrode, and the converted value is defined asthe first oxidation (or reduction) potential in the present invention.

An organic solvent for use in the measurement should be one having asufficiently low water content. The organic solvent may be one that cansatisfactorily dissolve a luminescent material or charge transportmaterial relating to the present invention therein, is resistant toelectrolytic oxidation (or reduction), and ensures a wide potentialwindow. Examples of such organic solvents include acetonitrile,methylene chloride, N,N-dimethylformamide, and tetrahydrofuran.

Individual components constituting a composition for an organicelectroluminescent device according to the present invention, and theconditions for their oxidation/reduction potentials, for example, willbe described below.

<Phosphorescent Material>

Any known materials are applicable as the phosphorescent material, andeach of such phosphorescent materials can be used alone or incombination. Phosphorescent materials are excellent from the viewpointof internal quantum efficiency. If a fluorescent material is used hereininstead of a phosphorescent material, the resulting device does noteffectively have an improved efficiency or a prolonged life, even thecondition between the charge transport material and the luminescentmaterial is satisfied.

It is important to reduce the molecular symmetry or rigidity of theluminescent material and/or to introduce a lipophilic substituent suchas an alkyl group into the luminescent material, in order to improve thesolubility in a solvent.

Preferred examples of phosphorescent materials include organometalliccomplexes each containing a metal selected from transition metalsbelonging to Group 7 to Group 11 of the periodic table (periodic tableof elements: IUPAC Periodic Table of the Elements, 2004).

Preferred metals in phosphorescent organometallic complexes eachcontaining a metal selected from transition metals belonging to Group 7to Group 11 of the periodic table include ruthenium, rhodium, palladium,silver, rhenium, osmium, iridium, platinum, and gold. Preferred examplesof these organometallic complexes include compounds represented byfollowing Formulae (4) and (5), and compounds described in PCTInternational Publication Numbers WO 2005/011370 and WO 2005/019373.

MG_((q-j))G′_(j)  (4)

In Formula (4), M represents a metal; “q” represents the valency of themetal M; G and G′ each represent a bidentate ligand; and “j” represents0, 1, or 2.

In Formula (5), M⁵ represents a metal; T represents carbon or nitrogen;and R⁹² to R⁹⁵ each independently represent a substituent, wherein R⁹⁴and R⁹⁵ are absent when T is nitrogen.

Initially, compounds represented by Formula (4) will be illustratedbelow.

In Formula (4), M represents any metal. Preferred examples thereofinclude the metals listed as the metals selected from Group 7 to Group11 of the periodic table.

The bidentate ligands G and G′ in Formula (4) each independentlyrepresent a ligand having the following partial structure:

From the viewpoint of stability of the complex, G′ is especiallypreferably:

In the partial structures in G and G′, Ring Q1 represents an aromatichydrocarbon group or an aromatic heterocyclic group, each of which mayhave a substituent; and Ring Q2 represents a nitrogen-containingaromatic heterocyclic group which may have a substituent.

The phrase “which may have a substituent” as used herein means “whichmay have one or more substituents”.

Preferred substituents on Rings Q1 and Q2 include halogen atoms such asfluorine atom; alkyl groups such as methyl group and ethyl group;alkenyl groups such as vinyl group; alkoxycarbonyl groups such asmethoxycarbonyl group and ethoxycarbonyl group; alkoxy groups such asmethoxy group and ethoxy group; aryloxy groups such as phenoxy group andbenzyloxy group; dialkylamino groups such as dimethylamino group anddiethylamino group; diarylamino groups such as diphenylamino group;carbazolyl group; acyl groups such as acetyl group; haloalkyl groupssuch as trifluoromethyl group; cyano group; and aromatic hydrocarbongroups such as phenyl group, naphthyl group, and phenantrhyl group.

More preferred examples of compounds represented by Formula (4) includecompounds represented by following Formulae (4a), (4b), and (4c):

In Formula (4a), M^(a) represents a metal as with M; q^(a) representsthe valency of the metal M^(a); Ring Q1 represents an aromatichydrocarbon group or an aromatic heterocyclic group, each of which mayhave a substituent; and Ring Q2 represents a nitrogen-containingaromatic heterocyclic group which may have a substituent.

In Formula (4b), M^(b) represents a metal as with M; q^(b) representsthe valency of the metal M^(b); Ring Q1 represents an aromatichydrocarbon group or an aromatic heterocyclic group, each of which mayhave a substituent; and Ring Q2 represents a nitrogen-containingaromatic heterocyclic group which may have a substituent.

In Formula (4c), M^(c) represents a metal as with M; q^(c) representsthe valency of the metal M^(c); “j” represents 0, 1, or 2; Ring Q1 andRing Q1′ each independently represent an aromatic hydrocarbon group oran aromatic heterocyclic group, each of which may have a substituent;and Ring Q2 and Ring Q2′ each independently represent anitrogen-containing aromatic heterocyclic group which may have asubstituent.

Preferred examples as Ring Q1 and Ring Q1′ in Formulae (4a), (4b), and(4c) include phenyl group, biphenyl group, naphthyl group,anthryl□group, thienyl group, furyl group, benzothienyl group,benzofuryl group, pyridyl group, quinolyl group, isoquinolyl group, andcarbazolyl group.

Preferred examples as Ring Q2 and Ring Q2′ include pyridyl group,pyrimidyl group, pyrazyl group, triazyl group, benzothiazolyl group,benzoxazolyl group, benzimidazolyl group, quinolyl group, isoquinolylgroup, quinoxalyl group, and phenanthrydyl group.

Examples of substituents which compounds represented by Formulae (4a),(4b), and (4c) may have include halogen atoms such as fluorine atom;alkyl groups such as methyl group and ethyl group; alkenyl groups suchas vinyl group; alkoxycarbonyl groups such as methoxycarbonyl group andethoxycarbonyl group; alkoxy groups such as methoxy group and ethoxygroup; aryloxy groups such as phenoxy group and benzyloxy group;dialkylamino groups such as dimethylamino group and diethylamino group;diarylamino groups such as diphenylamino group; carbazolyl group; acylgroups such as acetyl group; haloalkyl groups such as trifluoromethylgroup; and cyano group.

When the substituent is an alkyl group, it may generally have one ormore and six or less carbon atoms. When the substituent is an alkenylgroup, it may generally have two or more and six or less carbon atoms.When the substituent is an alkoxycarbonyl group, it may generally havetwo or more and six or less carbon atoms. When the substituent is analkoxy group, it may generally have one or more and six or less carbonatoms. When the substituent is an aryloxy group, it may generally havesix or more and fourteen or less carbon atoms. When the substituent is adialkylamino group, it may generally have two or more and twenty-four orless carbon atoms. When the substituent is a diarylamino group, it maygenerally have twelve or more and twenty-eight or less carbon atoms.When the substituent is an acyl group, it may generally have one or moreand fourteen or less carbon atoms. When the substituent is a haloalkylgroup, it may generally have one or more and twelve or less carbonatoms.

These substituents may be combined to form a ring. More specifically,for example, a substituent of Ring Q1 and a substituent of Ring Q2 maybe combined to form one condensed ring, or a substituent of Ring Q1′ anda substituent of Ring Q2′ may be combined to form one condensed ring. Anexample of the condensed ring includes 7,8-benzoquinoline group.

More preferred substituents on Ring Q1, Ring Q1′, Ring Q2, and Ring Q2′include alkyl groups, alkoxy groups, aromatic hydrocarbon groups, cyanogroup, halogen atoms, haloalkyl groups, diarylamino groups, andcarbazolyl group.

Preferred examples of M^(a), M^(b), and M^(c) in Formulae (4a), (4b),and (4c) include ruthenium, rhodium, palladium, silver, rhenium, osmium,iridium, platinum, and gold.

Specific examples of organometallic complexes represented by Formulae(4), (4a), (4b), and (4c) are illustrated below, which, however, are notlimitative at all. In the following formulae, Ph represents phenylgroup.

Of organometallic complexes represented by Formulae (4), (4a), (4b), and(4c), typically preferred are compounds each having, as ligand G and/orG′, a 2-arylpyridine ligand such as an 2-arylpyridine, an 2-arylpyridinederivative having any substituent, or an 2-arylpyridine derivativecondensed with any group.

Next, compounds represented by Formula (5) will be illustrated.

In Formula (5), M⁵ represents a metal, and specific examples thereofinclude the metals listed as the metal selected from metals belonging toGroup 7 to Group 11 of the periodic table. Among them, preferred areruthenium, rhodium, palladium, silver, rhenium, osmium, iridium,platinum, and gold, of which bivalent metals such as platinum andpalladium are more preferred.

In Formula (5), R⁹² and R⁹³ each independently represent hydrogen atom,a halogen atom, an alkyl group, an aralkyl group, an alkenyl group,cyano group, an amino group, an acyl group, an alkoxycarbonyl group,carboxyl group, an alkoxy group, an alkylamino group, an aralkylaminogroup, a haloalkyl group, hydroxyl group, an aryloxy group, an aromatichydrocarbon group, or an aromatic heterocyclic group.

When T is carbon, R⁹⁴ and R⁹⁵ each independently represent a substituentexemplified as with R⁹² and R⁹³. When T is nitrogen, R⁹⁴ and R⁹⁵ areabsent.

R⁹² to R⁹⁵ may each further have a substituent. There is no limitationon substituents which these groups may further have, and any groups canbe employed as the substituents.

Adjacent two of R⁹² to R⁹⁵ may be combined to form a ring.

Specific examples (5-a, 5-b, 5-c, 5-d, 5-e, 5-f, and 5-g) oforganometallic complexes represented by Formula (5) are illustratedbelow, which, however, are not limitative at all. In the followingformulae, Me represents methyl group, and Et represents ethyl group.

The molecular weight of a compound for use as a luminescent material inthe present invention is generally 10000 or less, preferably 5000 orless, more preferably 4000 or less, and further preferably 3000 or less,and is generally 100 or more, preferably 200 or more, more preferably300 or more, and further preferably 400 or more. If the molecular weightis less than 100, there may result in significant decrease of heatresistance, may cause gas generation, may invite decreased quality of afilm formed from the composition, or may cause morphological change ofthe resulting organic electroluminescent device due typically tomigration. If the molecular weight exceeds 10000, it may be difficult topurify the organic compound or it may possibly take a long time todissolve the organic compound in a solvent.

The first oxidation potential E_(D) ⁺ of a luminescent material for usein the present invention is generally 0.1 V or more, preferably 0.2 V ormore, more preferably 0.3 V or more, further preferably 0.4 V or more,and most preferably 0.5 V or more, and is generally 2.0 V or less,preferably 1.6 V or less, more preferably 1.4 V or less, furtherpreferably 1.2 V or less, and most preferably 1.0 V or less.

If the first oxidation potential of the luminescent material E_(D) ⁺ isless than 0.1 V, the first reduction potential of the luminescentmaterial E_(D) ⁻ must be set at a very low value. When this luminescentmaterial is used in an organic electroluminescent device, there mayresult in significant imbalance between positive and negative charges,or there may cause decreased durability of the luminescent materialagainst reduction, and the device may highly possibly fail to have asufficient luminance and/or a satisfactory life. In contrast, if thefirst oxidation potential of the luminescent material E_(D) ⁺ exceeds2.0 V, there may invite decreased durability of the luminescent materialagainst oxidation, and the device may highly possibly fail to have asufficient luminance and/or a satisfactory life.

The first reduction potential of the luminescent material E_(D) ⁻ foruse in the present invention is generally −3.0 V or more, preferably−2.8 V or more, more preferably −2.7 V or more, further preferably −2.6V or more, and most preferably −2.5 V or more, and is −1.0 V or less,preferably −1.2 V or less, more preferably −1.4 V or less, furtherpreferably −1.6 V or less, and most preferably −1.8 V or less.

If a luminescent material having a first reduction potential E_(D) ⁻less than −3.0 V is used in an organic electroluminescent device, theremay result in significant imbalance between positive and negativecharges, or there may cause decreased durability of the luminescentmaterial against reduction, and the device may highly possibly fail tohave a sufficient luminance and/or a satisfactory life. In contrast, ifa luminescent material having a first reduction potential E_(D) ⁻exceeding −1.0 V is used in an organic electroluminescent device, thefirst oxidation potential E_(D) ⁺ of the luminescent material must beset at a very high value, and there may invite decreased durability ofthe luminescent material against oxidation, and the device may highlypossibly fail to have a sufficient luminance and/or a satisfactory life.

<Charge Transport Material>

A charge transport material for use in the present invention desirablyhas at least one of the following functions:

(i) Injection function: the function of receiving a hole from an anodeor a hole injection layer when an electric field is applied, and/or thefunction of receiving an electron from a cathode or an electroninjection layer when an electric field is applied.

(ii) Transporting function: the function of transporting injectedcharges by the action of an electric field.

(iii) Light emitting function: the function of providing a field for therecombination between an electron and a hole and using this for thelight emission.

(iv) Blocking function: the function of controlling the transfer ofcharges so as to enable transportation and recombination of the chargesin good balance.

There may be a difference in easiness between the hole injection and theelectron injection, and there may be a difference in transportability asrepresented by mobility between hole and electron. However, a chargetransport material for use herein should essentially be capable ofefficiently transporting at least one of the two charges (hole andelectron).

From these viewpoints, the compound for use as a charge transportmaterial is typically preferably an organic compound represented byfollowing Formula (1):

(A)n−Z  (1)

In Formula (1), “A” represents an aromatic hydrocarbon group or anaromatic heterocyclic group;

“n” represents an integer of 1 or more and 10 or less;

“Z” represents a hydrogen atom or a substituent when “n” is 1, and “Z”represents a direct bond or a linkage group having a valency of “n” when“n” is 2 or more; and

when “n” is 2 or more, plural “A”s may be the same as or different fromeach other, and wherein “A” and “Z” may each further have a substituent.

Compounds represented by Formula (1) will be illustrated in detailbelow.

In Formula (1), “n” represents an integer which is generally 1 or more,and preferably 2 or more, and is generally 10 or less, and preferably 6or less. If the number “n” exceeds this range, it may be difficult toreduce impurities sufficiently through purification procedures. If “n”is less than this range, the charge injecting/transporting ability maybe significantly reduced.

When “n” is 1, “Z” is hydrogen atom or any substituent in Formula (1).When “Z” is a substituent, specific examples thereof include alkylgroups, alkenyl groups, alkynyl groups, amino groups,alkoxycarbonylamino groups, aryloxycarbonylamino groups, heterocyclicoxycarbonylamino groups, sulfonylamino groups, alkoxy groups, aryloxygroups, heterocyclic oxy groups, acyl groups, alkoxycarbonyl groups,aryloxycarbonyl groups, heterocyclic oxycarbonyl groups, acyloxy groups,sulfamoyl groups, carbamoyl groups, alkylthio groups, arylthio groups,heterocyclic thio groups, sulfonyl groups, sulfenyl groups, ureidogroups, phosphoramido groups, hydroxyl group, mercapto group, cyanogroup, sulfo group, carboxyl group, nitro group, hydroxamate group,sulfino group, hydrazino group, silyl groups, boryl groups, phosphinogroups, aromatic hydrocarbon groups, aromatic heterocyclic groups,groups represented by following Formula (2), and groups represented byfollowing Formula (3):

In Formula (2), R^(a) represents any substituent. The substituent R^(a)is generally a substituent having one or more and ten or less carbonatoms, and is preferably one having six or less carbon atoms. Specificexamples of R^(a) include alkyl groups, aralkyl groups, and aromatichydrocarbon groups.

In Formulae (2) and (3), R^(b), R^(c), and R^(d) each independentlyrepresent hydrogen atom or any substituent. When R^(b), R^(c), and R^(d)are arbitrary substituents, their carbon numbers and specific examplesare independently as with the carbon number and specific examples ofR^(a).

When Z is an alkyl group, it is a linear or branched alkyl group whichpreferably has one or more and thirty or less carbon atoms, and morepreferably has one or more and twelve or less carbon atoms. Examplesthereof include methyl, ethyl, n-propyl, 2-propyl, n-butyl, isobutyl,tert-butyl, and n-octyl groups.

When Z is an alkenyl group, it preferably has two or more carbon atomsand preferably has thirty or less, and further preferably twelve or lesscarbon atoms. Examples thereof include vinyl, allyl, and 1-butenylgroups.

When Z is an alkynyl group, it preferably has two or more and thirty orless carbon atoms, and further preferably has twelve or less carbonatoms. Example thereof include ethynyl and propargyl groups.

When Z is an amino group, it can also be an amino group substituted witha hydrocarbon group such as an alkyl group or an aromatic hydrocarbongroup. The amino group generally has zero or more and thirty-six or lesscarbon atoms, and preferably has twenty or less, and more preferablytwelve or less carbon atoms. Specific examples of such amino groupsinclude amino group, methylamino group, dimethylamino group, ethylaminogroup, diethylamino group, phenylamino group, diphenylamino group,dibenzylamino group, thienylamino group, dithienylamino group,pyridylamino group, and dipyridylamino group.

When Z is an alkoxycarbonylamino group, it generally has two or more andtwenty or less carbon atoms, and preferably has sixteen or less, andmore preferably twelve or less carbon atoms. Specific examples thereofinclude methoxycarbonylamino group.

When Z is an aryloxycarbonylamino group, it generally has seven or moreand twenty or less carbon atoms, and preferably has sixteen or less, andmore preferably twelve or less carbon atoms. Specific examples thereofinclude phenoxycarbonyl group.

When Z is a heterocyclic oxycarbonylamino group, it generally has two ormore, preferably five or more carbon atoms, and generally has twenty-oneor less, preferably fifteen or less, and more preferably eleven or lesscarbon atoms. Specific examples thereof include thienyloxycarbonylaminogroup.

When Z is a sulfonylamino group, it generally has one or more carbonatoms and generally has twenty or less, preferably sixteen or less, andmore preferably twelve or less carbon atoms. Specific examples thereofinclude methanesulfonylamino group, benzenesulfonylamino group, andthiophenesulfonylamino group.

When Z is an alkoxy group, it generally has one or more carbon atoms,and generally has twenty or less, preferably twelve or less, and morepreferably eight or less carbon atoms. Specific examples thereof includemethoxy group, ethoxy group, isopropoxy group, n-butoxy group, andt-butoxy group.

When Z is an aryloxy group, it generally has six or more carbon atoms,and generally has ten or less, preferably eight or less, and morepreferably six carbon atoms. Specific examples thereof include phenoxygroup.

When Z is a heterocyclic oxy group, it generally has one or more,preferably two or more, and more preferably four or more carbon atoms,and generally has ten or less, preferably eight or less, and morepreferably five or less carbon atoms. Specific examples thereof includethienyloxy group and pyridyloxy group.

When Z is an acyl group, it generally has one or more carbon atoms, andgenerally has twenty or less, preferably sixteen or less, and morepreferably twelve or less carbon atoms. Specific examples thereofinclude acetyl group, benzoyl group, formyl group, pivaloyl group,thenoyl group, and nicotinoyl group.

When Z is an alkoxycarbonyl group, it generally has two or more carbonatoms and generally has twenty or less, preferably sixteen or less, andmore preferably twelve or less carbon atoms. Specific examples thereofinclude methoxycarbonyl group and ethoxycarbonyl group.

When Z is an aryloxycarbonyl group, it generally has seven or morecarbon atoms, and generally has twenty or less, preferably sixteen orless, and more preferably seven carbon atoms. Specific examples thereofinclude phenoxycarbonyl group.

When Z is a heterocyclic oxycarbonyl group, it generally has two ormore, and preferably five or more carbon atoms, and generally has twentyor less, preferably twelve or less, and more preferably six or lesscarbon atoms. Specific examples thereof include thienyloxycarbonyl groupand pyridyloxycarbonyl group.

When Z is an acyloxy group, it generally has two or more carbon atoms,and generally has twenty or less, preferably sixteen or less, and morepreferably twelve or less carbon atoms. Specific examples thereofinclude acetoxy group, ethylcarbonyloxy group, benzoyloxy group,pivaloyloxy group, thenoyloxy group, and nicotinoyloxy group.

When Z is a sulfamoyl group, it can also be a sulfamoyl groupsubstituted with a hydrocarbon group such as an alkyl group or anaromatic hydrocarbon group. The sulfamoyl group generally has zero ormore carbon atom, and generally has twenty or less, and preferablytwelve or less carbon atoms. Specific examples thereof include sulfamoylgroup, methylsulfamoyl group, dimethylsulfamoyl group, phenylsulfamoylgroup, and thienylsulfamoyl group.

When Z is a carbamoyl group, it can also be a carbamoyl groupsubstituted with a hydrocarbon group such as an alkyl group or anaromatic hydrocarbon group. The carbamoyl group generally has one ormore carbon atoms, and generally has twenty or less, preferably sixteenor less, and more preferably twelve or less carbon atom. Specificexamples thereof include carbamoyl group, methylcarbamoyl group,diethylcarbamoyl group, and phenylcarbamoyl group.

When Z is an alkylthio group, it generally has one or more carbon atoms,and generally has twenty or less, preferably sixteen or less, and morepreferably twelve or less carbon atoms. Specific examples thereofinclude methylthio group, ethylthio group, and n-butylthio group.

When Z is an arylthio group, it generally has six or more carbon atoms,and generally has twenty-six or less, preferably twenty or less, andmore preferably twelve or less carbon atoms. Specific examples thereofinclude phenylthio.

When Z is a heterocyclic thio group, it generally has one or more,preferably two or more, and more preferably five or more carbon atoms,and generally has twenty-five or less, preferably nineteen or less, andmore preferably eleven or less carbon atoms. Specific examples thereofinclude thienylthio group and pyridylthio group.

When Z is a sulfonyl group, such sulfonyl groups further include asulfonyl group substituted with a hydrocarbon group such as an alkylgroup or an aromatic hydrocarbon group. The sulfamoyl group generallyhas one or more carbon atoms, and generally has twenty or less,preferably sixteen or less, and more preferably twelve or less carbonatoms. Specific examples thereof include tosyl group and mesyl group.

When Z is a sulfinyl group, it can also be a sulfinyl group substitutedwith a hydrocarbon group such as an alkyl group or an aromatichydrocarbon group. The sulfinyl group has one or more carbon atoms, andgenerally has twenty or less, preferably sixteen or less, and morepreferably twelve or less carbon atoms. Specific examples thereofinclude methylsulfinyl group and phenylsulfinyl group.

When Z is a ureido group, it can also be a ureido group substituted witha hydrocarbon group such as an alkyl group or an aromatic hydrocarbongroup. The ureido group generally has one or more carbon atoms, andgenerally has twenty or less, preferably sixteen or less, and morepreferably twelve or less carbon atoms. Specific examples thereofinclude ureido group, methylureido group, and phenylureido group.

When Z is a phosphoramido group, it can also be a phosphoramido groupsubstituted with a hydrocarbon group such as an alkyl group or anaromatic hydrocarbon group. The phosphoramido group generally has one ormore carbon atoms, and generally has twenty or less, preferably sixteenor less, and more preferably twelve or less carbon atoms. Specificexamples thereof include diethylphosphoramido group andphenylphosphoramido group.

When Z is a silyl group, it can also be a silyl group substituted with ahydrocarbon group such as an alkyl group or an aromatic hydrocarbongroup. The silyl group generally has one or more carbon atoms, andgenerally has ten or less, and preferably six or less carbon atoms.Specific examples thereof include trimethylsilyl group andtriphenylsilyl group.

When Z is a boryl group, it can also be a boryl group substituted with ahydrocarbon group such as an alkyl group or an aromatic hydrocarbongroup. The boryl group generally has one or more carbon atoms, andgenerally has ten or less, and preferably six or less carbon atoms.Specific examples thereof include dimesitylboryl group.

When Z is a phosphino group, it can also be a phosphino groupsubstituted with a hydrocarbon group such as an alkyl group or anaromatic hydrocarbon group. The phosphino group generally has one ormore carbon atoms, and generally has ten or less, and preferably six orless carbon atoms. Specific examples thereof include diphenylphosphinogroup.

When Z is an aromatic hydrocarbon group, it generally has six or morecarbon atoms, and generally has twenty or less, and preferably fourteenor less carbon atoms. Specific examples thereof include groups derivedfrom six-membered monocyclic rings, or bicyclic, tricyclic, tetracyclicor pentacyclic condensed rings containing such six-membered rings, suchas benzene ring, naphthalene ring, anthracene ring, phenanthrene ring,perylene ring, tetracene ring, pyrene ring, benzopyrene ring, chrysenering, triphenylene ring, and fluoranthene ring.

When Z is an aromatic heterocyclic group, constitutive hetero atomsthereof include nitrogen atom, oxygen atom, and sulfur atom. In thiscase, Z generally has one or more, preferably three or more carbonatoms, and generally has nineteen or less, and preferably thirteen orless carbon atoms. Specific examples thereof include groups derived fromfive-membered or six-membered monocyclic rings, or bicyclic, tricyclic,or tetracyclic condensed rings containing such five-membered orsix-membered rings, such as furan ring, benzofuran ring, thiophene ring,benzothiophene ring, pyrrole ring, pyrazole ring, oxazole ring,imidazole ring, oxadiazole ring, indole ring, carbazole ring,pyrroloimidazole ring, pyrrolopyrazole ring, pyrrolopyrrole ring,thienopyrrole ring, thienothiophene ring, furopyrrole ring, furofuranring, thienofuran ring, benzisoxazole ring, benzisothiazole ring,benzimidazole ring, pyridine ring, pyrazine ring, pyridazine ring,pyrimidine ring, triazine ring, quinoline ring, isoquinoline ring,cinnoline ring, quinoxaline ring, benzimidazole ring, perimidine ring,quinazoline ring, quinazolinone ring, and azulene ring.

When “n” is two or more, Z represents a direct bond or a linkage grouphaving a valency of “n”.

When Z is a linkage group having a valency of “n”, specific examplesthereof include a group represented by the following formula:

When Z is a linkage group having a valency of “n”, specific examples ofZ further include groups corresponding to the groups listed as thespecific examples of Z when Z is a substituent, except for removing(n−1) hydrogen atom(s) therefrom.

When Z is an alkynyl group, it generally has two or more carbon atoms,and generally has eight or less, and preferably four or less carbonatoms. Specific examples thereof include ethynyl group and propargylgroup.

Among them, Z is preferably an aromatic hydrocarbon group or an aromaticheterocyclic group, from the viewpoints of improving durability againstelectric oxidation/reduction and improving heat resistance.

Z may further have a substituent and/or may be condensed with anothergroup. When Z has two or more substituents, they may be the same as ordifferent from each other. If possible, these substituents may becombined with each other to form a ring.

Z may have any substituent(s) such as alkyl groups, alkenyl groups,alkynyl groups, aromatic hydrocarbon groups, acyl groups, alkoxy groups,aryloxy groups, alkylthio groups, arylthio groups, alkoxycarbonylgroups, aryloxycarbonyl groups, arylamino groups, alkylamino groups, andaromatic heterocyclic groups. Among them, alkyl groups, aromatichydrocarbon groups, and aromatic heterocyclic groups are preferred, ofwhich aromatic hydrocarbon groups are more preferred. Specific examplesof the substituents listed herein are as with the specific examples of Zwhen Z is a substituent.

Z may have any molecular weight. When Z is a substituent or a linkagegroup, the molecular weight thereof is generally 5000 or less, andpreferably 2000 or less.

In Formula (1), “A” represents any aromatic hydrocarbon group or anyaromatic heterocyclic group.

When “A” is an aromatic hydrocarbon group, it generally has six or morecarbon atoms, and generally has thirty or less, and preferably twenty orless carbon atoms. Specific examples thereof include groups derived fromsix-membered monocyclic rings, or bicyclic, tricyclic, tetracyclic, orpentacyclic fused rings containing such six-membered rings, such asbenzene ring, naphthalene ring, anthracene ring, phenanthrene ring,perylene ring, tetracene ring, pyrene ring, benzopyrene ring, chrysenering, triphenylene ring, and fluoranthene ring.

When “A” is an aromatic heterocyclic group, it generally has one ormore, and preferably three or more carbon atoms, and generally hastwenty-nine or less, and preferably nineteen or less carbon atoms.Specific examples thereof include groups derived from five-membered orsix-membered monocyclic rings, or bicyclic, tricyclic, or tetracyclicfused rings containing such five-membered or six-membered rings, such asfuran ring, benzofuran ring, thiophene ring, benzothiophene ring,pyrrole ring, pyrazole ring, oxazole ring, imidazole ring, oxadiazolering, indole ring, carbazole ring, pyrroloimidazole ring,pyrrolopyrazole ring, pyrrolopyrrole ring, thienopyrrole ring,thienothiophene ring, furopyrrole ring, furofuran ring, thienofuranring, benzisoxazole ring, benzisothiazole ring, benzimidazole ring,pyridine ring, pyrazine ring, pyridazine ring, pyrimidine ring, triazinering, quinoline ring, isoquinoline ring, cinnoline ring, quinoxalinering, benzimidazole ring, perimidine ring, quinazoline ring,quinazolinone ring, azulene ring, tetrazole ring, and imidazopyridinering.

Of the above listed groups, “A” is preferably a group derived frombenzene ring, naphthalene ring, pyridine ring, pyrimidine ring, pyrazinering, triazine ring, quinoline ring, isoquinoline ring, thiazole ring,oxazole ring, imidazole ring, indole ring, benzimidazole ring,imidazopyridine ring, or carbazole ring. This is from the points ofdurability against electric oxidation/reduction, and a wide band gapbetween the highest occupied molecular orbital (HOMO) and the lowestunoccupied molecular orbital (LUMO).

Of these, “A” is more preferably a group derived from benzene ring,naphthalene ring, pyridine ring, triazine ring, oxazole ring, thiazolering, imidazole ring, quinoline ring, isoquinoline ring, benzimidazolering, imidazopyridine ring, or carbazole ring, and is further morepreferably a group derived from benzene ring, pyridine ring, quinolinering, isoquinoline ring, benzimidazole ring, imidazopyridine ring, orcarbazole ring.

“A” is especially preferably a group derived from pyridine ring orcarbazole ring.

Of such groups derived from pyridine ring, bipyridyl group or a groupderived from a pyridine ring having substituent(s) at the 2-, 4-, and/or6-position of pyridine ring is preferred for more satisfactory stabilityagainst electric reduction. A substituent to be combined with thebipyridyl group or the group derived from a pyridine ring havingsubstituent(s) at the 2-, 4-, and/or 6-position of pyridine ring isarbitrary, but it is preferably an aromatic hydrocarbon group or anaromatic heterocyclic group.

In Formula (1), “A” may have a substituent. “A” may have anysubstituent, and specific examples of such substituents are as with theabove-listed substituents which Z may have. When “A” has two or moresubstituents, they may be the same as or different from each other. Ifpossible, these substituents may be combined with each other to form aring.

The molecular weight of “A” including its substituent(s) is generally5000 or less, and preferably 2000 or less.

Specific examples of “A” and Z will be illustrated below.

Initially, specific examples of “A” and Z when “n” is 1 include thefollowing groups R-1 to R-99. In the following specific examples, L¹,L², and L³ each independently represent hydrogen atom or anysubstituent. They are each independently preferably an alkyl group, anaromatic hydrocarbon group, or an aromatic heterocyclic group and mostpreferably phenyl group, from the viewpoint of electric durability. Thegroups listed herein may each further have a substituent, in addition toL¹, L², and L³.

Specific examples of Z when “n” is 2 or more include following bonds andlinkage groups, and each of these can be adopted alone, or two or moreof the same or different bonds or linkage groups can be combined to beadopted. In the following formulae, Z-1 represents a direct bond, andZ-2 to Z-187 each represent a linkage group. In the following specificexamples, L¹, L², and L³ each independently represent hydrogen atom orany substituent. They are each independently preferably an alkyl group,an aromatic hydrocarbon group, or an aromatic heterocyclic group, andare each most preferably phenyl group, from the viewpoint of electricdurability. The groups listed herein may each further have asubstituent, in addition to L¹, L², and L³.

Specific examples of compounds represented by Formula (1) areillustrated below.

Examples as carbazole compounds (including triarylamine compounds)include compounds described as charge transport materials typically inJapanese Unexamined Patent Application Publications No. 63-235946, No.2-285357, No. 2-261889, No. 3-230584, No. 3-232856, No. 5-263073, No.6-312979, No. 7-053950, No. 8-003547, No. 9-157643, No. 9-268283, No.9-165573, No. 9-249876, No. 9-310066, No. 10-041069, and No. 10-168447;EP Patent No. 847228; Japanese Unexamined Patent ApplicationPublications No. 10-208880, No. 10-226785, No. 10-312073, No. 10-316658,No. 10-330361, No. 11-144866, No. 11-144867, No. 11-144873, No.11-149987, No. 11-167990, No. 11-233260, and No. 11-241062; PCTInternational Publication Number WO-00/70655; U.S. Pat. No. 6,562,982;Japanese Unexamined Patent Application Publications No. 2003-040844, No.2001-313179, No. 2001-257076, and No. 2005-47811; Japanese PatentApplication No. 2003-204940; and Japanese Unexamined Patent ApplicationPublication No. 2005-068068.

Examples as phenylanthracene derivatives include compounds described ascharge transport materials typically in Japanese Unexamined PatentApplication Publication No. 2000-344691.

Examples as fused arylene star-burst compounds include compoundsdescribed as charge transport materials typically in Japanese UnexaminedPatent Application Publications No. 2001-192651 and No. 2002-324677.

Examples as fused imidazole compounds include compounds described ascharge transport materials typically in “Appl. Phys. Lett., vol. 78, p.1622, 2001”, Japanese Unexamined Patent Application Publication No.2001-335776, No. 2002-338579, No. 2002-319491, No. 2002-367785, and No.2002-367786.

Examples as azepine compounds include compounds described as chargetransport materials typically in Japanese Unexamined Patent ApplicationPublication No. 2002-235075.

Examples as fused triazole compounds include compounds described ascharge transport materials typically in Japanese Unexamined PatentApplication Publication No. 2002-356489.

Examples as propeller-like arylene compounds include compounds describedas charge transport materials typically in Japanese Unexamined PatentApplication Publication No. 2003-027048.

Examples as monotriarylamine compounds include compounds described ascharge transport materials typically in Japanese Unexamined PatentApplication Publications No. 2002-175883, No. 2002-249765, and No.2002-324676.

In addition, examples as arylbenzidine compounds include compoundsdescribed as charge transport materials typically in Japanese UnexaminedPatent Application Publication No. 2002-329577.

Examples as triarylboron compounds include compounds described as chargetransport materials typically in Japanese Unexamined Patent ApplicationPublications No. 2003-031367 and No. 2003-031368.

Examples as indole compounds include compounds described as chargetransport materials typically in Japanese Unexamined Patent ApplicationPublications No. 2002-305084, No. 2003-008866, and No. 2002-015871.

Examples as indolizine compounds include compounds described as chargetransport materials typically in Japanese Unexamined Patent ApplicationPublication No. 2000-311787.

Examples as pyrene compounds include compounds described as chargetransport materials typically in Japanese Unexamined Patent ApplicationPublication No. 2001-118682.

Examples as dibenzoxazole (or dibenzothiazole) compounds includecompounds described as charge transport materials typically in JapaneseUnexamined Patent Application Publication No. 2002-231453.

Examples as bipyridyl compounds include compounds described as chargetransport materials typically in Japanese Unexamined Patent ApplicationPublication No. 2003-123983.

Examples as pyridine compounds include compounds described as chargetransport materials typically in Japanese Unexamined Patent ApplicationPublications No. 2005-276801 and No. 2005-268199.

Of these, preferred examples are carbazole compounds (includingtriarylamine compounds), fused arylene star-burst compounds, fusedimidazole compounds, propeller-like arylene compounds, monotriarylaminecompounds, indole compounds, indolizine compounds, bipyridyl compounds,and pyridine compounds, from the point of excellent light emissionproperties when used in organic electroluminescent devices.

Among them, carbazole compounds, bipyridyl compounds, and pyridinecompounds are more preferred, and the combination use of a carbazolecompound with a bipyridyl compound or the combination use of a carbazolecompound and a pyridine compound is most preferred. This is because,when they are used in organic electroluminescent devices, the devicescan have further satisfactory operating lives. Likewise, compoundshaving both a carbazolyl group and a pyridyl group are preferably used.For example, the charge transport materials described in Japanese PatentApplications No. 2004-358592 and No. 2004-373981 are preferred.

It is also important to reduce the molecular symmetry or rigidity ofthese materials and/or to introduce a lipophilic substituent such as analkyl group into the materials, in order to improve the solubility in asolvent.

Specific examples of especially preferred compounds as the chargetransport material are illustrated below. In the following illustratedstructural formulae, —N-Cz represents N-carbazolyl group.

The glass transition point of a compound for use as the chargetransporting material is generally 70° C. or higher, preferably 100° C.or higher, more preferably 120° C. or higher, further preferably 130° C.or higher, and most preferably 150° C. or higher. If a compound havingan excessively low glass transition point is used in an organicelectroluminescent device, the device may have reduced heat resistanceand may possibly have a short operating life.

The molecular weight of a compound for use as the charge transportingmaterial in the present invention is generally 10000 or less, preferably5000 or less, more preferably 3000 or less, and is generally 100 ormore, preferably 300 or more, and more preferably 500 or more. If themolecular weight is less than 100, there may result in significantdecrease of heat resistance, may cause gas generation, may invitedecreased quality of a film formed from the composition, or may causemorphological change of the resulting organic electroluminescent devicedue typically to migration. If the molecular weight exceeds 10000, itmay be difficult to purify the organic compound or it may possibly takea long time to dissolve the organic compound in a solvent.

The band gap of a compound for use as the charge transport material inthe present invention is generally 3.0 V or more, preferably 3.2 V ormore, and more preferably 3.5 V or more. Blue-emitting fluorescentmaterials and phosphorescent materials typified by green toblue-emitting materials have large band gaps. When an organicelectroluminescent device is manufactured by using a phosphorescentmaterial of this type, a charge transporting material to be arrangedsurrounding the phosphorescent material preferably has a band gap equalto or larger than the band gap of the phosphorescent material, from thepoints of the luminous efficiency and life as an organicelectroluminescent device.

The first oxidation potential of a charge transporting material E_(T) ⁺for use in the present invention is generally 0.0 V or more, preferably0.1 V or more, more preferably 0.2 V or more, further preferably 0.3 Vor more, and most preferably 0.9 V or more, and is generally 2.1 V orless, preferably 1.7 V or less, more preferably 1.6 V or less, furtherpreferably 1.5 V or less, and most preferably 1.4 V or less.

If the first oxidation potential of the charge transporting materialE_(T) ⁺ is less than 0.0 V, the first reduction potential E_(T) ⁻ of thecharge transport material must be set at a very low value. When thismaterial is used in an organic electroluminescent device, there mayresult in significant imbalance between positive and negative charges,or there may cause decreased durability of the charge transport materialagainst reduction, and the device may highly possibly fail to have asufficient luminance and/or a satisfactory life. In contrast, if thefirst oxidation potential of the charge transport material E_(T) ⁺exceeds 2.1 V, there may invite decreased durability of the luminescentmaterial against oxidation, and the device may highly possibly fail tohave a sufficient luminance and/or a satisfactory life.

The first reduction potential of the charge transport material E_(T) ⁻as described in the present invention is generally −3.1 V or more,preferably −2.9 V or more, more preferably −2.8 V or more, furtherpreferably −2.7 V or more, and most preferably −2.1 V or more and isgenerally −0.9 V or less, preferably −1.1 V or less, more preferably−1.3 V or less, further preferably −1.5 V or less, and most preferably−1.7 V or less.

If a charge transport material having a first reduction potential E_(T)⁻ less than −3.1 V is used in an organic electroluminescent device,there may result in significant imbalance between positive and negativecharges, or there may cause decreased durability of the charge transportmaterial against reduction, and the device may highly possibly fail tohave a sufficient luminance and/or a satisfactory life. In contrast, ifa charge transport material having a first reduction potential E_(T) ⁻exceeding −0.9 V is used in an organic electroluminescent device, thefirst oxidation potential of the charge transport material E_(T) ⁺ mustbe set at a very high value, and there may invite decreased durabilityof the charge transport material against oxidation, and the device mayhighly possibly fail to have a sufficient luminance and/or asatisfactory life.

<First Oxidation Potential E_(D) ⁺ and First Reduction Potential E_(D) ⁻of Luminescent Material, and First Oxidation Potential E_(T) ⁺ and FirstReduction Potential E_(T) ⁻ of Charge Transport Material>

A layer referred to as a light emitting layer in an organicelectroluminescent device mainly contains a mixture of a luminescentmaterial called “dopant” and a charge transport material called “host”.In this case, the following pathway is regarded as a likely major lightemission mechanism.

Specifically, holes travel through the highest occupied molecularorbital (HOMO) of the charge transport material and come into thehighest occupied molecular orbital (HOMO) of the luminescent material.Electrons travel through the lowest unoccupied molecular orbital (LUMO)of the charge transporting material and come into the lowest unoccupiedmolecular orbital (LUMO) of the luminescent material. The holes andelectrons are then recombined as charges, to make the luminescentmaterial excited. At the time when the luminescent material undergoestransition from its excited state to its ground state, the luminescentmaterial emits electromagnetic waves (light) corresponding to the energydifference between the two states.

The “HOMO level” herein corresponds to the first oxidation potential ofeach material, and the “LUMO level” corresponds to the first reductionpotential of each material.

Accordingly, it has been believed in related art that a luminescentmaterial in an electrically neutral state is preferably more susceptibleto electron donation (oxidation) and electron acceptation (reduction)than a charge transport material. Specifically, the first oxidationpotential of the luminescent material E_(D) ⁺, the first reductionpotential of the luminescent material E_(D) ⁻, the first oxidationpotential of the charge transport material E_(T) ⁺, and the firstreduction potential of the charge transporting material E_(T) ⁻ inrelated art generally satisfy the following condition:

E_(T) ⁻<E_(D) ⁻<E_(D) ⁺<E_(T) ⁺

However, according to the present invention, a luminescent material anda charge transport material are selected so as to allow the firstoxidation potential of the luminescent material E_(D) ⁺, the firstreduction potential of the luminescent material E_(D) ⁻, the firstoxidation potential of the charge transport material E_(T) ⁺, and thefirst reduction potential of the charge transport material E_(T) ⁻ tosatisfy the following condition:

E _(T) ⁻+0.1≦E _(D) ⁻ <E _(T) ⁺ ≦E _(D) ⁺−0.1

or

E _(D) ⁻+0.1≦E _(T) ⁻ <E _(D) ⁺ ≦E _(T) ⁺−0.1

(1) In the case when the parameters satisfy the condition: E_(T)⁻+0.1≦E_(D) ⁻<E_(T) ⁺≦E_(D) ⁺−0.1

A possible mechanism in this case is as follows. Electrons travelthrough the charge transport material to the luminescent material in anelectrically neutral state earlier than holes do, and the electrons aretrapped in the lowest unoccupied molecular orbital (LUMO) of theluminescent material; and thereafter holes are injected into a bondingorbital having the highest energy level in the resulting luminescentmaterial in an anionic state. The bonding orbital corresponds to thehighest occupied molecular orbital (HOMO) of the luminescent material ina neutral state.

Specifically, it is primarily important that the first reductionpotential of the luminescent material E_(D) ⁻ is necessarily andsufficiently larger than the first reduction potential of the chargetransport material E_(T) ⁻. In other words, it is important that theluminescent material is necessarily and sufficiently more susceptible toelectron acceptation but more resistant to electron donation than thecharge transport material. In addition, it is also important that thefirst oxidation potential of the luminescent material E_(D) ⁺ ismoderately larger than the first oxidation potential of the chargetransport material E_(T) ⁺. Namely, it is important that the chargetransport material is more likely to accept and transport holes.

Based on the above description, the absolute value of the differencebetween E_(D) ⁻ and E_(T) ⁻ |E_(D) ⁻−E_(T) ⁻| is preferably 0.1 V ormore, more preferably 0.15 V or more, and most preferably 0.2 V or more.The absolute value |E_(D) ⁻−E_(T) ⁻| is preferably 1.5 V or less, morepreferably 1.0 V or less, and most preferably 0.5 V or less. If theabsolute value |E_(D) ⁻−E_(T) ⁻| is lower than the lower limit, theelectron may not be firmly trapped by the luminescent material in anelectrically neutral state, there may occur a decreased probability ofcharge recombination on the luminescent material, and this may causedecreased luminous efficiency of the organic electroluminescent device.If the absolute value |E_(D) ⁻−E_(T) ⁻| exceeds the upper limit, thedrive voltage of the device may significantly increase due to increasedvoltage loss.

The absolute value of the deference between E_(T) ⁺ and E_(D) ⁻ |E_(T)⁺−E_(D) ⁻| is preferably 1.0 V or more, more preferably 1.5 V or more,and most preferably 2.0 V or more. The absolute value |E_(T) ⁺−E_(D) ⁻|is preferably 4.5 V or less, more preferably 3.5 V or less, and mostpreferably 3.0 V or less. If the absolute value |E_(T) ⁺−E_(D) ⁻| isless than the lower limit, the device may show a decreased luminousefficiency, or may operate at a significantly increased drive voltagedue to increased voltage loss. If the absolute value |E_(T) ⁺−E_(D) ⁻|exceeds the upper limit, the device may operate a significantlyincreased drive voltage.

The absolute value of the difference between E_(D) ⁺ and E_(T) ⁺ |E_(D)⁺−E_(T) ⁺| is preferably 0.1 V or more, more preferably 0.15 V or more,and most preferably 0.2 V or more. The absolute value |E_(D) ⁺−E_(T) ⁺|is preferably 1.5 V or less, more preferably 1.0 V or less, and mostpreferably 0.5 V or less. If the absolute value |E_(D) ⁺−E_(T) ⁺| isless than the lower limit, holes can be easily injected not only intothe highest occupied molecular orbital (HOMO) of the charge transportingmaterial in an electrically neutral state but also into the highestoccupied molecular orbital (HOMO) of the luminescent material in anelectrically neutral state, and this may cause a decreased probabilityof charge recombination to thereby cause a decreased luminous efficiencyof the organic electroluminescent device. If the absolute value |E_(D)⁺−E_(T) ⁺| exceeds the upper limit, this may seriously hinder the chargerecombination on the luminescent material to thereby cause a decreasedluminous efficiency of the device.

The absolute value of the difference between E_(T) ⁻ and E_(D) ⁺ |E_(T)⁻−E_(D) ⁺| is preferably 1.5 V or more, more preferably 2.5 V or more,and most preferably 3.0 V or more. The absolute value |E_(T) ⁻−E_(D) ⁺|is preferably 5.5 V or less, more preferably 4.5 V or less, and mostpreferably 4.0 V or less. If the absolute value |E_(T) ⁻−E_(D) ⁺| isless than the lower limit, there may fail to provide a device thatefficiently emit light in the visible ray region. If the absolute value|E_(T) ⁻−E_(D) ⁺| exceeds the upper limit, the drive voltage of thedevice may significantly increase.

(2) In the case when the parameters satisfy the condition: E_(D)⁻+0.1≦E_(T) ⁻<E_(D) ⁺≦E_(T) ⁺−0.1

A possible mechanism in this case is as follows. Holes travel throughthe charge transport material to the luminescent material in anelectrically neutral state earlier than electrons do, and the holes aretrapped in the highest occupied molecular orbital (HOMO) of theluminescent material; and thereafter holes are injected into ananti-bonding orbital having the lowest energy level in the resultingluminescent material in a cationic state. The anti-bonding orbitalcorresponds to the lowest unoccupied molecular orbital (LUMO) of theluminescent material in a neutral state.

Specifically, it is primarily important that the first oxidationpotential of the luminescent material E_(D) ⁺ is necessarily andsufficiently smaller than the first oxidation potential of the chargetransport material E_(T) ⁺. In other words, it is important that theluminescent material is more susceptible to hole acceptation but moreresistant to hole donation (hole release) than the charge transportmaterial. In addition, it is also important that the first reductionpotential of the luminescent material E_(D) ⁻ is moderately smaller thanthe first reduction potential of the charge transport material E_(T) ⁻.Namely, it is important that the charge transport material is morelikely to accept and transport electrons.

Based on the above description, the absolute value of the differencebetween E_(D) ⁺ and E_(T) ⁺ |E_(D) ⁺−E_(T) ⁺| is preferably 0.1 V ormore, more preferably 0.15 V or more, and most preferably 0.2 V or more.The absolute value |E_(D) ⁺−E_(T) ⁺| is also preferably 1.5 V or less,more preferably 1.2 V or less, and most preferably 0.9 V or less. If theabsolute value |E_(D) ⁺−E_(T) ⁺| is less than the lower limit, the holemay not firmly trapped by the luminescent material in an electricallyneutral state, there may occur a decreased probability of chargerecombination on the luminescent material, and this may cause decreasedluminous efficiency of the organic electroluminescent device. If theabsolute value |E_(D) ⁺−E_(T) ⁺| exceeds the upper limit, the drivevoltage of the device may significantly increase due to increasedvoltage loss.

The absolute value of the difference between E_(D) ⁺ and E_(T) ⁻ |E_(D)⁺−E_(T) ⁻| is preferably 1.0 V or more, more preferably 1.5 or more, andmost preferably 2.0 V or more. The absolute value |E_(D) ⁺−E_(T) ⁻| isalso preferably 4.5 V or less, more preferably 3.5 V or less, and mostpreferably 3.0 or less. If the absolute value |E_(D) ⁺−E_(T) ⁻| is lessthan the lower limit, the luminous efficiency of the device maydecrease, or the drive voltage of the device may significantly increasedue to increased voltage loss. If the absolute value |E_(D) ⁺−E_(T) ⁻|exceeds the upper limit, the drive voltage of the device maysignificantly increase.

The absolute value of the difference between E_(D) ⁻ and E_(T) ⁻ |E_(D)⁻−E_(T) ⁻| is preferably 0.10 V or more, more preferably 0.15 V or more,and most preferably 0.20 V or more. The absolute value |E_(D) ⁻−E_(T) ⁻|is also preferably 1.5 V or less, more preferably 1.0 V or less, andmost preferably 0.5 V or less. If the absolute value |E_(D) ⁻−E_(T) ⁻|is less than the lower limit, electrons can be easily injected not onlyinto the charge transporting material in an electrically neutral statebut also into the luminescent material in an electrically neutral state,and this may cause a decreased probability of charge recombination tothereby cause a decreased luminous efficiency of the organicelectroluminescent device. If the absolute value |E_(D) ⁻−E_(T) ⁻|exceeds the upper limit, this may seriously hinder the chargerecombination on the luminescent material to thereby cause a decreasedluminous efficiency of the device.

The absolute value of the difference between E_(T) ⁺ and E_(D) ⁻ |E_(T)⁺−E_(D) ⁻| is preferably 1.5 V or more, more preferably 2.5 V or more,and most preferably 3.0 V or more. The absolute value |E_(T) ⁺−E_(D) ⁻|is also preferably 5.5 V or less, more preferably 4.5 V or less, andmost preferably 4.0 V or less. If the absolute value |E_(T) ⁺−E_(D) ⁻|is less than the lower limit, there may fail to provide a device thatefficiently emit light in the visible ray region. If the absolute value|E_(T) ⁺−E_(D) ⁻| exceeds the upper limit, the drive voltage of thedevice may significantly increase.

[Comparison in Voltage when Composition for Organic ElectroluminescentDevice Contains Two or More Diffident Luminescent Materials and ChargeTransport Materials]

<In the Case when Composition for Organic Electroluminescent DeviceAccording to the Present Invention Contains Two or More Different ChargeTransport Materials>

When the parameters satisfy the condition: E_(D) ⁻+0.1≦E_(T) ⁻<E_(D)⁺≦E_(T) ⁺−0.1, the “first oxidation potential of the charge transportmaterial E_(T) ⁺” refers to the first oxidation potential of a chargetransport material which has the smallest first oxidation potential(namely, a material which is most susceptible to oxidation). The “firstreduction potential of the charge transport material E_(T) ⁻” refers tothe first reduction potential of a charge transport material which hasthe largest first reduction potential (namely, a material which is mostsusceptible to reduction). When the parameters satisfy the condition:E_(T) ⁻+0.1≦E_(D) ⁻<E_(T) ⁺≦E_(D) ⁺−0.1, the “first oxidation potentialof the charge transport material E_(T) ⁺” to the first oxidationpotential of a charge transport material which has the smallest firstoxidation potential (namely, a material which is most susceptible tooxidation). The “first reduction potential of the charge transportmaterial E_(T) ⁻” refers to the first reduction potential of a chargetransport material which has the largest first reduction potential(namely, a material which is most susceptible to reduction).

<In the Case when Composition for Organic Electroluminescent DeviceAccording to the Present Invention Contains Two or More DifferentLuminescent Materials>

When the parameters satisfy the condition: E_(T) ⁻+0.1≦E_(D) ⁻<E_(T)⁺≦E_(D) ⁺−0.1, the “first oxidation potential of the luminescentmaterial E_(D) ⁺” refers to the first oxidation potential of aluminescent material which has the smallest first oxidation potential(namely, a material which is most susceptible to oxidation), and the“first reduction potential of the luminescent material E_(D) ⁻” refersto the first reduction potential of a luminescent material which has thelargest first reduction potential (namely, a material which is mostsusceptible to reduction).

When the parameters satisfy the condition: E_(D) ⁻+0.1≦E₁ ⁻<E_(D)⁺≦E_(T) ⁺−0.1, the “first oxidation potential of the luminescentmaterial E_(D) ⁺” refers to the first oxidation potential of aluminescent material which has the smallest first oxidation potential(namely, a material which is most susceptible to oxidation), and the“first reduction potential of the luminescent material” refers to thefirst reduction potential of a luminescent material E_(D) ⁻ which hasthe largest first reduction potential (namely, a material which is mostsusceptible to reduction).

<Solvent>

Solvents to be contained in a composition for an organicelectroluminescent device according to the present invention are notspecifically limited, as long as the solutes can be satisfactorilydissolved therein. However, since most of materials for organicelectroluminescent devices generally have aromatic rings, typicalexamples of solvents for use herein include aromatic hydrocarbons suchas toluene, xylenes, mesitylene, cyclohexylbenzene, and tetralin;halogenated aromatic hydrocarbons such as chlorobenzene,dichlorobenzene, and trichlorobenzene; aromatic ethers such as1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, phenetole,2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene,2,3-dimethylanisole, 2,4-dimethylanisole, and diphenyl ether; aromaticesters such as phenyl acetate, phenyl propionate, methyl benzoate, ethylbenzoate, ethyl benzoate, propyl benzoate, and n-butyl benzoate;alicyclic ketones such as cyclohexanone and cyclooctanone; and alicyclicalcohols such as cyclohexanol and cyclooctanol.

When the solute molecule has a suitable substituent such as an estergroup or an ether group, examples of solvents for use herein alsoinclude, in addition to the above-listed solvents, aliphatic ketonessuch as methyl ethyl ketone and dibutyl ketone; aliphatic alcohols suchas butanol and hexanol; aliphatic ethers such as ethylene glycoldimethyl ether, ethylene glycol diethyl ether, and propyleneglycol-1-monomethyl ether acetate (PGMEA); and aliphatic esters such asethyl acetate, n-butyl acetate, ethyl lactate, and n-butyl lactate.

When a solvent excessively evaporates from a composition for an organicelectroluminescent device during wet coating process, the stability infilm-formation may deteriorate. To avoid this, solvents each having aboiling point of 100° C. or higher, preferably a boiling point of 150°C. or higher, and more preferably a boiling point of 200° C. or higherare effective. In addition, a solvent must evaporate at a suitable ratefrom a liquid film immediately after film-formation in order to yield amore homogenous film. For this purpose, the solvent generally has aboiling point of 80° C. or higher, preferably a boiling point of 100° C.or higher, more preferably a boiling point of 120° C. or higher andgenerally has a boiling point of lower than 270° C., preferably aboiling point of lower than 250° C., and more preferably a boiling pointof lower than 230° C.

If the composition contains water, the water may remain in a film afterdrying to thereby adversely affect the properties of an organicelectroluminescent device, because most of materials typically in acathode of such an organic electroluminescent device significantlydeteriorate due to water. Examples of a procedure for reducing the watercontent in the solution (composition) include sealing with nitrogen gas,the use of a drying agent, predehydration of a solvent, and the use of asolvent having a low water solubility. Among them, the use of a solventhaving a low water solubility is preferred, because this preventswhitening of a film of the solution due to absorption of water from theatmosphere during a wet film-formation step. From these viewpoints, acomposition for an organic electroluminescent device according to thisembodiment preferably contains 10 percent by weight or more of a solventhaving a solubility in water at 25° C. of 1 percent by weight or less,preferably 0.1 percent by weight or less.

When a solvent satisfies all these requirements, i.e., the solubility ofthe solute, the evaporation rate, and water solubility, it may be usedalone. When, however, it is difficult to select such a solventsatisfying all the requirements, two or more different solvents may beused in combination.

<Other Components>

A composition for an organic electroluminescent device according to thepresent invention may further contain other solvents in addition to thesolvents as listed above. Examples of such other solvents include amidessuch as N,N-dimethylformamide and N,N-dimethylacetamide; and dimethylsulfoxide.

The composition may further contain various additives such as levelingagents and antifoaming agents.

When two or more layers are laminated through wet coating process, theselayers may be dissolved in each other. To avoid this, the compositionmay contain a photo-curable resin and/or a thermosetting resin, so as tocure the composition after coating to be insoluble. The resin for useherein such as a photo-curable resin and/or a thermosetting resin isgenerally a resin having a first oxidation potential E_(x) ⁺ and a firstreduction potential E_(x) ⁻ and satisfying the following conditions:

E _(x) ⁻ <E _(T) ⁻ and E _(D) ⁺ <E _(x) ⁺ when E _(T) ⁻+0.1≦E _(D) ⁻ <E_(T) ⁺ ≦E _(D) ⁺−0.1;

or a resin having a first oxidation potential E_(x) ⁺ and a firstreduction potential E_(x) ⁻ and satisfying the following conditions:

E _(x) ⁻ <E _(D) ⁻ and E _(T) ⁺ <E _(x) ⁺ when E _(D) ⁻+0.1≦E _(T) ⁻ <E_(D) ⁺ ≦E _(T) ⁺−0.1.

<Contents and Proportions of Materials in Composition for OrganicElectroluminescent Device>

The solid content including a luminescent material, a charge transportmaterial, and an additional component to be added according tonecessity, such as a leveling agent, in a composition for an organicelectroluminescent device is generally 0.01 percent by weight or more,preferably 0.05 percent by weight or more, more preferably 0.1 percentby weight or more, further preferably 0.5 percent by weight or more, andmost preferably 1 percent by weight or more, and is generally 80 percentby weight or less, preferably 50 percent by weight or less, morepreferably 40 percent by weight or less, further preferably 30 percentby weight or less, and most preferably 20 percent by weight or less. Ifthe content is less than 0.01 percent by weight, it may be difficult toform a thick film from the composition. If the content exceeds 80percent by weight, it may be difficult to form a thin film from thecomposition.

The weight ratio of a luminescent material to a charge transportingmaterial in a composition for an organic electroluminescent deviceaccording to the present invention is generally 0.1/99.9 or more, morepreferably 0.5/99.5 or more, further preferably 1/99 or more, and mostpreferably 2/98 or more, and is generally 50/50 or less, more preferably40/60 or less, further preferably 30/70 or less, and most preferably20/80 or less. If the ratio is less than 0.1/99.9 or exceeds 50/50, theluminous efficiency may seriously decrease.

<Preparation Method of Composition for Organic ElectroluminescentDevice>

A composition for an organic electroluminescent device according to thepresent invention may be prepared by dissolving solutes such as aluminescent material and a charge transporting material, and additivessuch as a leveling agent and an anti-foaming agent added according tonecessity, in a suitable solvent. The solutes are generally dissolvedwith stirring the mixture so as to shorten the time necessary for thedissolving step and to uniformize the concentrations of solutes in thecomposition. The dissolving step may be carried out at ordinarytemperature, or carried out with heating so as to accelerate dissolutionwhen the dissolution rate is low. After the completion of the dissolvingstep, the composition may be subjected to a filtrating step such asfiltering according to necessity.

<Properties and Physical Properties of Composition for OrganicElectroluminescent Device>

Water Content

The water content of the composition as a solution is preferablyminimized, because, if the composition contains water upon wetfilm-formation for forming a film in an organic electroluminescentdevice, water migrates into the formed film to thereby impair theuniformity of the film. In addition, generally most of materialstypically in a cathode of an organic electroluminescent device maydeteriorate due to water. Accordingly, if the composition containswater, water may remain in a film after drying and may possibly impairthe properties of the device.

Specifically, the water content of a composition for an organicelectroluminescent device according to the present invention isgenerally 1 percent by weight or less, preferably 0.1% or less, and morepreferably 0.01% or less.

The water content of the composition is preferably analyzed according tothe method specified in Japanese Industrial Standards (JIS) “Testmethods for water content of chemical products” (JIS K0068:2001). It canbe analyzed typically by Karl-Fischer reagent method (JIS K0211-1348).

Concentration of Primary Amine- and Secondary Amine-Containing Compounds

A composition for an organic electroluminescent device according to thepresent invention preferably has a low concentration of a primary amine-and secondary amine-containing compounds, because such primary amine-and secondary amine-containing compounds have lower charge transportingability, are more likely to act as a charge trap, and are moresusceptible to decomposition reaction such as proton detachment thantertiary amine compounds.

More specifically, the concentration of nitrogen atoms derived fromprimary amino group (—NH₂) and secondary amino group (>NH) is preferably100 ppm (μg/g) or less, and more preferably 10 ppm (μg/g) or less, basedon the total weight of materials other than solvents.

The “primary amine-containing compound” in a composition for an organicelectroluminescent device refers to a compound which contains one ormore nitrogen atoms, in which at least one of the nitrogen atom(s) iscombined with two hydrogen atoms and one atom other than hydrogen.Namely, the primary amine-containing compound is a compound representedby RNH₂, wherein R represents any group other than hydrogen atom.

The “secondary amine-containing compound” refers to a compound whichcontains one or more nitrogen atoms, in which at least one of thenitrogen atom(s) is combined with one hydrogen atom and two atoms otherthan hydrogen. Namely, the secondary amine-containing compound is acompound represented by RR′NH, wherein R and R′ each independentlyrepresent any group other than hydrogen atom, or R and R′ may becombined to form a ring.

Examples of procedures for identifying primary amine- and secondaryamine-containing compounds include processes using magnetic resonancesystems (NMR (¹H-NMR and ¹³C-NMR)) and Fourier transform infraredspectrophotometers (FT-IR), as well as mass spectrometry (MS, LC/MS,GC/MS, and MS/MS). Where necessary, other apparatuses can be used incombination. Examples of such apparatuses include gas chromatographs(GC), high-performance liquid chromatographs (HPLC), high-performanceamino acid analyzers (AAA), capillary electrophoresis measurementsystems (CE), size exclusion chromatographs (SEC), gel permeationchromatographs (GPC), cross fractionation chromatographs (CFC),ultraviolet-visible ray-near infrared spectrophotometers (UV.VIS, NIR),and electron spin resonance spectrometers (ESR).

Known techniques can be applied to the separation of primary amine- andsecondary amine-containing compounds. Examples of such techniquesinclude the techniques described in “Handbook of Separation/PurificationTechnology” (1993, edited by the Chemical Society of Japan),“High-purity Separation of Trace Components and Difficult-to-SeparateSubstances by Chemical Conversion” (1988, published by IPC Co., Ltd.),and “Experimental Chemistry (Fourth Ed.) Vol. 1; Section: Separation andPurification” (1990, edited by the Chemical Society of Japan).

Specific examples of purification procedures include variouschromatography techniques, extraction, adsorption, occlusion, melting orfusion, crystallization, distillation, evaporation, sublimation, ionexchange, dialysis, filtration, ultrafiltration, reverse osmosis,pressurized osmosis, zone melting, electrophoresis, centrifugation,floatation separation, sedimentation, and magnetic separation. Suchchromatography techniques are classified by shape into column, paper,thin-layer, and capillary chromatography; by mobile phase into gas,liquid, micelle, and supercritical fluid chromatography; and byseparation mechanism into adsorption, partition, ion-exchange, molecularsieve, chelate, gel filtration, exclusion, and affinity chromatography.

Examples of processes for detecting/determining primary amine- andsecondary amine-containing compounds include:

i) a process of subjecting a sample with concentrated sulfuric acid toignition decomposition to thereby convert them into ammonium sulfate,adjusting the decomposition mixture to be strongly basic, distillingammonia through steam distillation, and trapping ammonia in a sulfuricacid or boric acid solution having a known concentration;

ii) a process of oxidatively decomposing a sample with basic potassiumperoxodisulfate into nitric acid ion, adjusting the pH of the resultingsolution to 2 to 3, and determining absorbance of nitric acid ion at awavelength of 220 nm to thereby determine the nitrogen concentration(ultraviolet absorptiometry);

iii) a process for the detection by using an electrogeneratedchemiluminescence reaction with Ru(II) bipyridine complex as a detectionreagent, described in Japanese Unexamined Patent Application PublicationNo. 4-315048; and

iv) a process for the detection using a surface ionization detector(SID), described in Japanese Unexamined Patent Application PublicationNo. 10-115606.

Uniformity

A composition for an organic electroluminescent device according to thepresent invention is preferably a homogenous liquid at ordinarytemperature. Thus, the stability increases in wet film-formation. Forexample, when the composition is discharged from a nozzle according toan ink-jet process, the discharge stability increases. The phrase“homogenous liquid at ordinary temperature” means that the compositionis a liquid of a homogenous phase and does not contain particlecomponents having a size of 0.1 μm or more.

Physical Properties

If a composition for an organic electroluminescent device according tothe present invention has an extremely low viscosity, a film of thecomposition formed in a film-formation step, for example, may haveexcessively high flowability to thereby cause an uneven film surface, orthe composition may not be satisfactorily discharged from a nozzle inink-jet film-formation. In contrast, if the composition has an extremelyhigh viscosity, it may often cause plugging of a nozzle in ink-jetfilm-formation. Consequently, the viscosity of a composition accordingto the present invention at 25° C. is generally 2 mPa·s or more,preferably 3 mPa·s or more, and more preferably 5 mPa·s or more, and isgenerally 1000 mPa·s or less, preferably 100 mPa·s or less, and morepreferably 50 mPa·s or less.

The surface tension at 20° C. of a composition for an organicelectroluminescent device according to the present invention isgenerally less than 50 mN/m, and preferably less than 40 mN/m. This isbecause, if the composition has a high surface tension and is used as acomposition for film-formation on a substrate, the composition may havepoor wettability, and a film formed from the composition may have poorleveling property to thereby often cause an uneven surface of the filmafter drying.

The vapor pressure at 25° C. of a composition for an organicelectroluminescent device according to the present invention isgenerally 50 mmHg or less, preferably 10 mmHg or less, and morepreferably 1 mmHg or less. This is because, if the composition has ahigh vapor pressure, for example, the composition may often undergochange in concentrations of the solutes due to evaporation of thesolvent.

<Storage of Composition for Organic Electroluminescent Device>

A composition for an organic electroluminescent device according to thepresent invention is preferably stored by placing in a vessel thatblocks ultraviolet transmission, such as a brown glass bottle, andhermetically sealing the vessel. The storage temperature is generally−30° C. or higher, and preferably 0° C. or higher, and is generally 35°C. or lower, and preferably 25° C. or lower.

[Thin Film for Organic Electroluminescent Device]

A thin film for an organic electroluminescent device according to thepresent invention is generally used as an organic light emitting layerof an organic electroluminescent device.

The refractive index of a thin film for an organic electroluminescentdevice according to the present invention is preferably 1.78 or lesswith respect to light with a wavelength of 500 nm to 600 nm.

The refractive index of the film is determined, for example, byspectroscopic ellipsometry or prism coupling. The spectroscopicellipsometry for use in determination of the refractive index in thepresent invention will be illustrated in detail below.

In the spectroscopic ellipsometry, a change in polarization of lightreflected from the surface of a sample. Optical constants are determinedby optimizing parameters of a suitable model function indicating theoptical constants so as to reproduce actually measured values of Ψ andΔ.

Such optical constants are generally in the form of smooth functionswith respect to wavelengths, and their real part and imaginary part havea causal relation called Kramers-Kronig relation. Accordingly, theoptical constants of most materials can be modeled as functions.

Representative model functions for use in analyses by spectroscopicellipsometry are as follows:

Cauchy model typically for a transparent body or a transparent film;

Lorentz model typically for a metal film or a transparent conductivefilm; and

Parameterized Semiconductor model typically for a semiconductor materialor a transparent film.

According to the spectroscopic ellipsometry, optical constants(refractive index n and extinction coefficient k) as bulk or as a thinfilm can be determined at wavelengths in the near ultraviolet, visible,and near infrared regions (300 to 1700 nm), and the thickness (d) of asingle layer or a multilayer film can be determined in the range of, forexample, several nanometers to several micrometers.

The values Ψ and Δ can be determined with high precision and highreproducibility according to spectroscopic ellipsometry, because ratiosare measured in the spectroscopic ellipsometric determination.

Wet film-formation is desirable as a film-formation process for yieldinga thin film for an organic electroluminescent device having a refractiveindex within the preferred range.

The film-formation of a thin film for an organic electroluminescentdevice (hereinafter also referred to as “organic layer”) using acomposition for an organic electroluminescent device according to thepresent invention is preferably carried out through wet film-formation.Such a wet film-formation process can be selected according to theproperties of materials to be contained in the composition and of asubstrate as a base material from among, for example, spin coating,spray coating, an ink-jet process, flexographic printing, and screenprinting. A film formed by such a film-formation process is preferablydried through heating so as to reduce water and residual solventcontained in the film. The drying through heating is carried out byusing a heating device or procedure such as a hot plate or an oven, orby induction heating. The heating treatment is preferably carried out at60° C. or higher for sufficient effects, and is more preferably carriedout at 100° C. or higher for reducing the content of residual water. Theheating time is generally about one minute to about eight hours.

When an organic layer is formed through wet film-formation on an anodetypically of indium tin oxide (ITO), the anode may be treated with aspecific halogen compound, such as 4-trifluoromethylbenzoyl chlorideshown below, immediately before the film-formation as disclosed inJapanese Unexamined Patent Application Publication No. 2002-270369. Thistreatment enables easy injection of holes from the anode. Specifically,when ITO is treated with an acid chloride having an electron withdrawinggroup, such as the following compound, the anode surface is modifiedwith the compound having an electron withdrawing group to thereby forman electric double layer on the anode surface. An electric fieldgenerated by the action of the electric double layer increases the workfunction of the anode and hence enables easy injection of holes from theanode.

The film may be subjected to a surface treatment typically for improvingthe leveling property of the film and for improving the coatabilitytypically through reduction of crawling. Examples of such surfacetreatments include UV/ozone treatment, oxygen plasma treatment, hydrogenplasma treatment, and hexamethyldisilazane (HMDS) treatment. Each ofthese surface treatments can be used in combination.

Residual water, if contained in an organic layer thus formed, is notdesirable, because the residual water may adversely affect theproperties of the device, as described above. More specifically, thewater content in the resulting organic layer is 1000 ppm by weight orless, preferably 100 ppm by weight or less, and more preferably 10 ppmby weight or less. A residual solvent derived from the composition, ifremains in the organic layer, is also not desirable. This is because theresidual solvent may often cause migration of materials constituting theorganic layer, due to heat generated upon energizing of the organicelectroluminescent device or due to elevated temperatures in theenvironment where the device is used. Specifically, the content ofresidual solvent in the organic layer is 1000 ppm by weight or less,preferably 100 ppm by weight or less, and more preferably 10 ppm byweight or less.

The contents of water and residual solvent in the organic layer can beanalyzed typically by programmed thermal desorption-mass spectrometry(TPD-MS).

[Transfer Member for Thin Film for Organic Electroluminescent Device]

Such a transfer member is a member used as an image-imparting elementfor transferring an image pattern to an image-receiving elementaccording to laser induced thermal imaging process (LITI process). Thistechnique is widely used in the fields typically of printing,composition (typesetting), and photography.

FIG. 1 illustrates a typical configuration of a transfer member for athin film for an organic electroluminescent device according to thepresent invention. With reference to FIG. 1, a transfer member 11includes a base material 12, and a photothermal conversion layer 13, anintermediate layer 14, and a transfer layer 15 arranged sequentially onthe base material 12. The transfer layer 15 is melted as a result ofheating by the action of the photothermal conversion layer 13 and istransferred as a pattern onto an image-receiving element (not shown). Atransfer member for a thin film for an organic electroluminescent deviceaccording to the present invention may further arbitrarily include oneor more additional layers according to necessity.

The base material 12 in a transfer member for a thin film for an organicelectroluminescent device according to the present invention can beformed from any natural or synthetic material, as long as it satisfiesrequirements for a transfer member for a thin film for an organicelectroluminescent device. Requirements for the base material include,for example, transparency to laser light and heat resistance, becauseheating for transfer of an image component is carried out by theapplication of laser light. The requirements also include moderateflexibility, lightness, handleability, and mechanical strength, becausethe transfer member is applied to an image-receiving element upon useand removed therefrom after use. A transparent polymer is preferablyused as the base material. Examples thereof include polyesters such aspoly(ethylene terephthalate)s; acrylic resins; polyepoxys (epoxyresins); polyethylenes; and polystyrenes, of which poly(ethyleneterephthalate)s are more preferably used. The thickness of the basematerial can be arbitrarily adjusted according typically to thespecifications of a desired transfer member for a thin film for anorganic electroluminescent device, and is generally within a range of0.01 to 1 mm.

The photothermal conversion layer 13 supported by the base material 12acts to receive applied laser light, convert the optical energy intothermal energy, melt the image component in the transfer layer 15 facingthe photothermal conversion layer 13 with the interposition of theintermediate layer 14, and transfer and solidify the molten imagecomponent to the surface of the image receiving element. Consequently,the photothermal conversion layer 13 preferably includes alight-absorptive material such as a metal layer (film) composed ofaluminum, oxide and/or sulfide thereof; carbon black; graphite; or aninfrared dye, or includes a layer containing a dispersedlight-absorptive material. The photothermal conversion layer 13preferably contains a photo-induced polymerizable component for curingthe layer. When a photothermal conversion layer 13 is formed as themetal layer (film) as the light-absorptive layer, it is suitably formedto a thickness of 100 to 5000 angstroms by vacuum deposition, electronbeam deposition, or sputtering.

Preferred examples of the photothermal conversion layer 13 also includea layer containing a carbon black, a photo-induced polymerizable monomeror oligomer, and/or photopolymerization initiator dispersed in a binderresin. Such a photothermal conversion layer 13 of components dispersedin a binder resin can be generally formed, for example, by applying aresin composition having a predetermined composition to a surface of thebase material 12 according to a known coating process such as spincoating, gravure printing, or die coating, and drying the applied film.The thickness of the photothermal conversion layer 13 of componentsdispersed in a binder resin can be set within a wide range dependingtypically on the specifications and advantages of a desired transfermember for a thin film for an organic electroluminescent device. Thethickness is generally within a range of 0.001 to 10 μm.

The intermediate layer 14 arranged between the photothermal conversionlayer 13 and the transfer layer 15 especially acts to uniformize thephotothermal conversion action of the photothermal conversion layer 13.The layer can be generally formed from a resin material satisfying theabove-mentioned requirements. The intermediate layer 14 can be generallyformed, for example, by applying a resin composition having apredetermined composition to a surface of the photothermal conversionlayer 13 according to a known coating process such as spin coating,gravure printing, or die coating, and drying the applied film, in thesame manner as the photothermal conversion layer 13. The thickness ofthe intermediate layer 14 can be set within a wide range dependingtypically on desired effects and is generally within a range of 0.05 to10 μm.

The structure of a transfer member for a thin film for an organicelectroluminescent device can be modified according to its use. Forexample, the transfer member for a thin film for an organicelectroluminescent device may have an antireflection coating so as toprevent the properties of the transfer layer 15 from decreasing due toreflection, and/or it may have a gas generation layer instead of theintermediate layer 14, so as to improve the sensitivity of the transfermember.

When the gas generation layer absorbs light or heat, it decomposes todischarge nitrogen gas or hydrogen gas to thereby provide transferringenergy. Examples of the gas generation layer include at least onematerial selected from pentaerythritol tetranitrate (PETN) andtrinitrotoluene (TNT).

The transfer layer 15 is arranged as a topmost layer of the transfermember 11 for a thin film for an organic electroluminescent deviceaccording to the present invention. This layer is an electroluminescentthin film which is melted by the action of the photothermal conversionlayer 13 or is delaminated by the action of a vaporized gas generationlayer and is transferred as a pattern to an image-receiving element, asis described above. It corresponds to a thin film for an organicelectroluminescent device according to the present invention and can beformed as a film by the above-mentioned process.

[Organic Electroluminescent Device]

An organic electroluminescent device according to the present inventionis an organic electroluminescent device including a substrate bearing ananode, a cathode, and an organic light emitting layer arranged betweenthe two electrodes, in which the organic light emitting layer is a layerformed through wet film-formation using the composition for an organicelectroluminescent device according to the present invention, or is alayer formed by using the transfer member for a thin film for an organicelectroluminescent device according to the present invention.

FIG. 2 is a cross-sectional view schematically illustrating a structureof a general organic electroluminescent device for use in the presentinvention. FIG. 2 shows a substrate 1, an anode 2, a hole injectionlayer 3, an organic light emitting layer 4, an electron injection layer5, and a cathode 6.

<Substrate>

The substrate 1 functions as a support in the organic electroluminescentdevice and includes a plate of quartz or glass, a metal plate or metalfoil, or a plastic film or sheet. In particular, a glass plate and aplate or film of transparent synthetic resin such as a polyester, apolymethacrylate, a polycarbonate or a polysulfone are preferred. When asynthetic resin substrate is used, its gas barrier properties areimportant. If the gas barrier properties are too poor, the organicelectroluminescent device may deteriorate due to the air outside havingpassed through the substrate, thus poor gas barrier properties not beingpreferred. To avoid this, for example, a dense silicon oxide film may bepreferably arranged on at least one side of the synthetic resinsubstrate to thereby ensure sufficient gas barrier properties.

<Anode>

An anode 2 is arranged on the substrate 1. The anode 2 serves to injectholes into a hole transport layer 4. The anode 2 generally includes ametal such as aluminum, gold, silver, nickel, palladium or platinum; ametal oxide such as indium oxide and/or tin oxide; a metal halide suchas copper iodide; carbon black; or a conductive polymer such aspoly(3-methylthiophene), polypyrrole or polyaniline. The anode 2 isgenerally formed by sputtering or vacuum deposition. When the anode 2 isformed from fine particles of a metal such as silver, fine particles ofcopper iodide, carbon black, fine particles of a conductive metal oxide,or fine particles of a conductive polymer, it can also be formed bydispersing such particles in a suitable binder resin solution to yield adispersion, and coating the dispersion on the substrate 1. Further, whenthe anode 2 is formed from an electroconductive polymer, the anode 2 canalso be directly formed as a polymerized thin film on the substrate 1through electrolytic polymerization or formed by applying anelectroconductive polymer to the substrate 1 (App. Phys. Lett., vol. 60,p. 2711, 1992). The anode 2 may be of a multilayer structure made fromtwo or more different materials.

The thickness of the anode 2 varies depending upon requiredtransparency. When some transparency is required, the transmittance forvisible light is adjusted to be usually 60% or more, and preferably 80%or more. In this case, the thickness of the anode is usually 5 nm ormore, and preferably 10 nm or more, and is usually 1,000 nm or less, andpreferably 500 nm or less. When the anode may be opaque, the anode 2 mayalso function as the substrate 1. In addition, a layer of anotherelectroconductive material may be arranged on the anode 2.

The surface of the anode is preferably subjected to an ultraviolet ray(UV)/ozone treatment or a treatment with oxygen plasma or argon plasmato remove impurities deposited on the anode and to adjust ionizationpotential to thereby carry out hole injection more satisfactorily.

<Hole Injection Layer>

An organic electroluminescent device according to the present inventionpreferably further includes a hole injection layer between the organiclight emitting layer and the anode.

Since the hole injection layer 3 is a layer which functions to transportholes from the anode 2 to the organic light emitting layer 4, the holeinjection layer 3 preferably contains a hole-transporting compound.

A hole is transported in such a manner that one electron is removed froman electrically neutral compound to yield a cation radical, and thecation radical receives one electron from a neighboring electricallyneutral compound. If the hole injection layer does not contain a cationradical compound when the device is not energized, a hole-transportingcompound gives an electron to the anode to thereby form a cation radicalof the hole-transporting compound, and the cation radical receives anelectron from another electrically neutral hole-transporting compound tothereby transport a hole.

The hole injection layer preferably contains a cation radical compound.This is because, when the hole injection layer 3 contains a cationradical compound, a cation radical necessary for hole transportation ispresent in a concentration equal to or higher than the concentrationthereof formed as a result of the oxidation of the anode 2, and thisimproves the hole-transporting ability. The hole injection layer morepreferably contains both a cation radical compound and ahole-transporting compound, because an electron can be smoothlyreceived/given when an electrically neutral hole-transporting compoundis present in the vicinity of a cation radical compound.

The “cation radical compound” herein is an ionic compound containing acation radical and a counter anion, which cation radical is a chemicalspecies corresponding to a hole-transporting compound, except forremoving one electron therefrom. The cation radical compound already hasan easy-to-move hole (free carrier).

The hole injection layer 3 also preferably contains a hole-transportingcompound and an electron-accepting compound. This is because the cationradical compound is formed by mixing a hole-transporting compound withan electron-accepting compound to thereby cause one electron to transferfrom the hole-transporting compound to the electron-accepting compound.

Summarizing preferred materials as mentioned above, the hole injectionlayer 3 preferably contains a hole-transporting compound and morepreferably contains both a hole-transporting compound and anelectron-accepting compound. The hole injection layer 3 also preferablycontains a cation radical compound and more preferably contains both acation radical compound and a hole-transporting compound.

Where necessary, the hole injection layer 3 further contains acoatability improver and/or a binder resin that hardly acts as a chargetrap.

It is also possible, however, that an electron-accepting compound aloneis applied as the hole injection layer 3 to the anode 2 by wetfilm-formation, and a composition for an organic electroluminescentdevice according to the present invention is directly applied to thehole injection layer 3. In this case, part of the composition for anorganic electroluminescent device according to the present inventioninteracts with the electron-accepting compound to thereby constitute alayer having excellent hole injection ability.

Hole-Transporting Compound

The hole-transporting compound is preferably a compound having anionization potential between those of the anode 2 and the organic lightemitting layer 4. More specifically, the hole-transporting compound ispreferably a compound having an ionization potential of 4.5 eV to 6.0eV.

Examples thereof include aromatic amine compounds, phthalocyaninederivatives or porphyrin derivatives, oligothiophene derivatives, andpolythiophene derivatives, of which aromatic amine compounds arepreferred for their non-crystallinity and transmittance to visible rays.

Of aromatic amine compounds, aromatic tertiary amine compounds are morepreferred. The “aromatic tertiary amine compounds” herein refer tocompounds having aromatic tertiary amine structures and also includecompounds each having a group derived from an aromatic tertiary amine.

While types of such aromatic tertiary amine compounds are notspecifically limited, more preferred are polymeric compounds(polymerized organic compounds having sequential repeating units) eachhaving a weight-average molecular weight of 1000 or more and 1000000 orless, from the point of effectively smoothing the surface of the layer.

Preferred examples of such polymeric aromatic tertiary amine compoundsinclude polymeric compounds each having a repeating unit represented byfollowing General Formula (6):

In General Formula (6), Ar²¹ and Ar²² each independently represent anaromatic hydrocarbon group which may have a substituent, or an aromaticheterocyclic group which may have a substituent; Ar²³ to Ar²⁵ eachindependently represent a bivalent aromatic hydrocarbon group which mayhave a substituent, or a bivalent aromatic heterocyclic group which mayhave a substituent; and Y represents a linkage group selected from thefollowing Group Y1 of linkage groups, where two groups of Ar²¹ to Ar²⁵bound to the same nitrogen atom may be combined to form a ring.

In the above formulae, Ar³¹ to Ar⁴¹ each independently represent amonovalent or bivalent group which may have a substituent and is derivedfrom an aromatic hydrocarbon ring or an aromatic heterocyclic ring; andR³¹ and R³² each independently represent hydrogen atom or anysubstituent.

The groups Ar²¹ to Ar²⁵ and Ar³¹ to Ar⁴¹ can each be a monovalent orbivalent group derived from any aromatic hydrocarbon ring or anyaromatic heterocyclic ring. These may be different from or the same withone another. They may each have any substituent.

Examples of such aromatic hydrocarbon rings include five- orsix-membered monocyclic rings, or bicyclic, tricyclic, tetracyclic, orpentacyclic condensed rings containing such five- or six-membered rings.Specific examples thereof include benzene ring, naphthalene ring,anthracene ring, phenanthrene ring, perylene ring, tetracene ring,pyrene ring, benzopyrene ring, chrysene ring, triphenylene ring,acenaphthene ring, fluoranthene ring, and fluorene ring.

Examples of aromatic heterocyclic rings include five- or six-memberedmonocyclic rings, or bicyclic, tricyclic, or tetracyclic condensed ringscontaining such five- or six-membered rings. Specific examples thereofinclude furan ring, benzofuran ring, thiophene ring, benzothiophenering, pyrrole ring, pyrazole ring, imidazole ring, oxadiazole ring,indole ring, carbazole ring, pyrroloimidazole ring, pyrrolopyrazolering, pyrrolopyrrole ring, thienopyrrole ring, thienothiophene ring,furopyrrole ring, furofuran ring, thienofuran ring, benzisoxazole ring,benzisothiazole ring, benzimidazole ring, pyridine ring, pyrazine ring,pyridazine ring, pyrimidine ring, triazine ring, quinoline ring,isoquinoline ring, cinnoline ring, quinoxaline ring, phenanthridinering, benzimidazole ring, perimidine ring, quinazoline ring,quinazolinone ring, and azulene ring.

The groups Ar²³ to Ar²⁵, Ar³¹ to Ar³⁵, and Ar³⁷ to Ar⁴⁰ can also begroups each containing two or more groups combined with each other, thegroups being selected from one or more of bivalent groups derived fromthe above-illustrated aromatic hydrocarbon rings and/or aromaticheterocyclic rings.

The groups as Ar²¹ to Ar⁴¹ derived from aromatic hydrocarbon ringsand/or aromatic heterocyclic rings may each further have a substituent.The molecular weight of the substituent is generally about 400 or less,and is preferably about 250 or less. The substituent is not specificallylimited in its type and can be, for example, one or more substituentsselected from following Group W of Substituents.

[Group W of Substituents]

Group W of Substituents includes methyl group, ethyl group, and otheralkyl groups generally having one or more carbon atoms, and generallyten or less, and preferably eight or less carbon atoms; vinyl group andother alkenyl groups generally having two or more carbon atoms, andgenerally having eleven or less, and preferably five or less carbonatoms; ethynyl group and other alkynyl groups generally having two ormore carbon atoms, and generally having eleven or less, and preferablyfive or less carbon atoms; methoxy group, ethoxy group, and other alkoxygroups generally having one or more carbon atoms, and generally havingten or less, and preferably six or less carbon atoms; phenoxy group,naphthoxy group, pyridyloxy group, and other aryloxy groups generallyhaving four or more, and preferably five or more carbon atoms, andgenerally having twenty-five or less, and preferably fourteen or lesscarbon atoms; methoxycarbonyl group, ethoxycarbonyl group, and otheralkoxycarbonyl groups generally having two or more carbon atoms, andgenerally having eleven or less, and preferably seven or less carbonatoms; dimethylamino group, diethylamino group, and other dialkylaminogroups generally having two or more carbon atoms, and generally havingtwenty or less, and preferably twelve or less carbon atoms;diphenylamino group, ditolylamino group, N-carbazolyl group, and otherdiarylamino groups generally having ten or more, preferably twelve ormore carbon atoms, and generally having thirty or less, and preferablytwenty-two or less carbon atoms; phenylmethylamino group and otherarylalkylamino groups generally having six or more, preferably seven ormore carbon atoms, and generally having twenty-five or less, andpreferably seventeen or less carbon atoms; acetyl group, benzoyl group,and other acyl groups generally having two or more carbon atoms, andgenerally having ten or less, and preferably seven or less carbon atoms;fluorine atom, chlorine atom, and other halogen atoms; trifluoromethylgroup and other haloalkyl groups generally having one or more carbonatoms, and generally having eight or less, and preferably four or lesscarbon atoms; methylthio group, ethylthio group, and other alkylthiogroups generally having one or more carbon atoms, and generally havingten or less, and preferably six or less carbon atoms; phenylthio group,naphthylthio group, pyridylthio group, and other arylthio groupsgenerally having four or more, preferably five or more carbon atoms, andgenerally having twenty-five or less, and preferably fourteen or lesscarbon atoms; trimethylsilyl group, triphenylsilyl group, and othersilyl groups generally having two or more, preferably three or morecarbon atoms, and generally having thirty-three or less, and preferablytwenty-six or less carbon atoms; trimethylsiloxy group, triphenylsiloxygroup, and other siloxy groups generally having two or more, preferablythree or more carbon atoms, and generally having thirty-three or less,and preferably twenty-six or less carbon atoms; cyano group; phenylgroup, naphthyl group, and other aromatic hydrocarbon cyclic groupsgenerally having six or more carbon atoms, and generally having thirtyor less, and preferably eighteen or less carbon atoms; and thienylgroup, pyridyl group, and other aromatic heterocyclic groups generallyhaving three or more, preferably four or more carbon atoms, andgenerally having twenty-eight or less, and preferably seventeen or lesscarbon atoms.

Preferred as the groups Ar²¹ and Ar²² are monovalent groups derived frombenzene ring, naphthalene ring, phenanthrene ring, thiophene ring, andpyridine ring, of which monovalent groups derived from phenyl group andnaphthyl group are more preferred, from the points of the solubility,heat resistance, and hole injection/transporting ability of thepolymeric compounds.

Preferred as the groups Ar²³ to Ar²⁵ are bivalent groups derived frombenzene ring, naphthalene ring, anthracene ring, and phenanthrene ring,of which bivalent groups derived from phenylene group, biphenylenegroup, and naphthylene group are more preferred, from the points of theheat resistance and the hole injection/transporting ability includingoxidation/reduction potentials.

The groups R³¹ and R³² may be the same as or different from each otherand can each be hydrogen atom or any substituent. The substituentsherein are not specifically limited in their types, and applicablesubstituents include alkyl groups, alkenyl groups, alkynyl groups,alkoxy groups, silyl groups, siloxy groups, aromatic hydrocarbon groups,aromatic heterocyclic groups, and halogen atoms. Specific examplesthereof include the groups as listed in Group W of Substituents.

Specific examples and preferred examples of polymeric aromatic tertiaryamine compounds each having a repeating unit represented by GeneralFormula (6) include, but are not limited to, those described in PCTInternational Publication Number WO 2005/089024.

Preferred examples of polymeric aromatic tertiary amine compoundsfurther include polymeric compounds containing repeating unitsrepresented by following General Formula (7) and/or (8):

In General Formulae (7) and (8), Ar⁴⁵, Ar⁴⁷ and Ar⁴⁸ each independentlyrepresent an aromatic hydrocarbon group which may have a substituent, oran aromatic heterocyclic group which may have a substituent; Ar⁴⁴ andAr⁴⁶ each independently represent a bivalent aromatic hydrocarbon groupwhich may have a substituent, or a bivalent aromatic heterocyclic groupwhich may have a substituent, wherein two groups of Ar⁴⁵ to Ar⁴⁸ boundto the same nitrogen atom may be combined to form a ring; and R⁴¹ to R⁴³each independently represent hydrogen atom or any substituent.

Specific examples, preferred examples, examples of substituents whichthey may have, and examples of preferred substituents of Ar⁴⁵, Ar⁴⁷, andAr⁴⁸, and Ar⁴⁴ and Ar⁴⁶ are as with those of Ar²¹ and Ar²², and Ar²³ toAr²⁵, respectively. The groups R⁴¹ to R⁴³ are preferably hydrogen atomsor substituents listed in [Group W of Substituents], of which hydrogenatoms, alkyl groups, alkoxy groups, amino groups, aromatic hydrocarbongroups, and aromatic hydrocarbon groups are more preferred.

Specific examples and preferred examples of polymeric aromatic tertiaryamine compounds each containing repeating units represented by GeneralFormula (7) and/or (8) include, but are not limited to, those describedin PCT International Publication Number WO 2005/089024.

When the hole injection layer is formed through wet film-formation, ahole-transporting compound that is highly soluble in various solvents ispreferably used. From this viewpoint, preferred examples of aromatictertiary amine compounds include binaphthyl compounds represented byfollowing General Formula (9) (Japanese Unexamined Patent ApplicationPublication No. 2004-014187) and unsymmetrical 1,4-phenylenediaminecompounds represented by following General Formula (10) (JapaneseUnexamined Patent Application Publication No. 2004-026732). The materialfor use herein can also be selected as a compound that is highly solublein various solvents, from among compounds used as materials for formingthin films having hole injection/transporting ability in known organicelectroluminescent devices.

In General Formula (9), Ar⁵¹ to Ar⁵⁴ each independently represent anaromatic hydrocarbon group which may have a substituent, or an aromaticheterocyclic group which may have a substituent; two groups of Ar⁵¹ toAr⁵⁴ bound to the same nitrogen atom may be combined to form a ring; X¹and X² each independently represent a direct bond or a bivalent linkagegroup; “u” and “v” each independently represent an integer of 0 or moreand 4 or less, wherein “u” and “v” satisfy the condition: u+v≧1, andwherein the naphthalene rings in General Formula (9) may each have asubstituent, in addition to —X¹NAr^(5l)Ar⁵² and —X²NAr⁵³Ar⁵⁴.

In General Formula (10), Ar⁵⁵, Ar⁵⁶, and Ar⁵⁷ each independentlyrepresent an aromatic hydrocarbon group which may have a substituent, oran aromatic heterocyclic group which may have a substituent, and each ofthese has a total of ten or more carbon atoms, in which Ar⁵⁶ and Ar⁵⁷bound to the same nitrogen atom may be combined to form a ring.

Specific examples, preferred examples, examples of substituents whichthey may have, and examples of preferred substituents of Ar⁵¹ to Ar⁵⁷are as with those of Ar²¹ and Ar²², respectively. The groups Ar⁵¹ andAr⁵³ are typically preferably aromatic hydrocarbon groups having adiarylamino group substituted at the para-position, such as4-(diphenylamino)phenyl group.

The numbers “u” and “v” are preferably both 1.

X¹ and X² are each preferably a direct bond or a bivalent linkage groupderived from an aromatic hydrocarbon ring and are most preferably bothdirect bonds.

The naphthalene rings in General Formula (9) may each have anysubstituent, in addition to —X¹NAr⁵¹Ar⁵² and —X²NAr⁵³Ar⁵⁴. Thesubstituents —X¹NAr⁵¹Ar⁵² and —X²NAr⁵³Ar⁵⁴ may be substituted at anypositions of the naphthalene rings but are preferably substituted at the4- and 4′-positions of the naphthalene rings in binaphthyl compoundsrepresented by General Formula (9).

The binaphthylene structures in compounds represented by General Formula(9) preferably have substituents at the 2- and/or 2′-position. Examplesof such substituents at the 2- and/or 2′-position include alkyl groups,alkoxy groups, alkenyl groups, and alkoxycarbonyl groups, each of whichmay have a substituent.

The binaphthylene structures in compounds represented by General Formula(9) may have any substituents in addition to those at the 2- and2′-positions. Examples of the substituents include the groups listed asthe substituents at the 2- and 2′-positions. Compounds represented byGeneral Formula (9) are supposed to have high solubility, because thetwo naphthalene rings are distorted with respect to each other. Thecompounds, if having substituents at the 2- and 2′-positions, aresupposed to have further higher solubility, because the two naphthalenerings are further distorted with respected to each other.

The compounds represented by General Formula (10) are supposed to havehigh solubility in solvents, because they do not have symmetry of C2 orhigher. Unsymmetrical diamine compounds represented by following GeneralFormula (11) are also preferred, because they are supposed to be highlysoluble in various solvents for the same reason as above.

In General Formula (11), Ar⁵⁸ to Ar⁶¹ each independently represent anaromatic hydrocarbon group which may have a substituent, or an aromaticheterocyclic group which may have a substituent; Ar⁶² represents abivalent aromatic hydrocarbon group which may have a substituent, or abivalent aromatic heterocyclic group which may have a substituent,wherein two of Ar⁵⁸ to Ar⁶¹ bound to the same nitrogen atom may becombined to form a ring, and wherein Ar⁵⁸ is a group different from anyof Ar⁵⁹ to Ar⁶¹.

Specific examples, preferred examples, examples of substituents whichthey may have, and examples of preferred substituents of Ar⁵⁸ to Ar⁶¹are as with those of Ar²¹ and Ar²². Specific examples, preferredexamples, examples of substituents which they may have, and examples ofpreferred substituents of Ar⁶² are as with those of Ar²³ to Ar²⁵.

The molecular weights of the compounds represented by General Formulae(9), (10), and (11) are each generally less than 5000, preferably lessthan 2500 and are generally 200 or more, preferably 400 or more.

Specific examples and preferred examples of the compounds represented byGeneral Formulae (9), (10), and (11) include, but are not limited to,those described in Japanese Patent Application No. 2005-21983.

Such aromatic amine compounds usable as the hole-transporting compoundin the hole injection layer further include known compounds used asmaterials for forming layers having hole injection/transporting abilityin organic electroluminescent devices. Examples thereof include aromaticdiamine compounds each including a series of aromatic tertiary amineunits, such as 1,1-bis(4-di-p-tolylaminophenyl)cyclohexane (JapaneseUnexamined Patent Application Publication No. 59-194393); aromatic aminecompounds containing two or more tertiary amines and having two or morecondensed aromatic rings substituted on nitrogen atom, typified by4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (Japanese UnexaminedPatent Application Publication No. 5-234681); aromatic triaminecompounds as triphenylbenzene derivatives having a starburst structure(U.S. Pat. No. 4,923,774); aromatic diamine compounds such asN,N′-diphenyl-N,N′-bis(3-methylphenyl)biphenyl-4,4′-diamine (U.S. Pat.No. 4,764,625);α,α,α′,α-′tetramethyl-α,α′-bis(4-di(p-tolyl)aminophenyl)-p-xylene(Japanese Unexamined Patent Application Publication No. 3-269084);triphenylamine derivatives which are three-dimensionally unsymmetricalas the whole molecules (Japanese Unexamined Patent ApplicationPublication No. 4-129271); compounds each containing a pyrenyl groupsubstituted with two or more aromatic diamino groups (JapaneseUnexamined Patent Application Publication No. 4-175395); aromaticdiamine compounds each containing tertiary aromatic amine units combinedwith each other through ethylene group (Japanese Unexamined PatentApplication Publication No. 4-264189); aromatic diamines having styrylstructures (Japanese Unexamined Patent Application Publication No.4-290851); compounds each containing aromatic tertiary amine unitscombined with each other through thiophene group (Japanese UnexaminedPatent Application Publication No. 4-304466); star-burst aromatictriamine compounds (Japanese Unexamined Patent Application PublicationNo. 4-308688); benzylphenyl compounds (Japanese Unexamined PatentApplication Publication No. 4-364153); compounds each containingtertiary amines combined with each other through fluorene group(Japanese Unexamined Patent Application Publication No. 5-25473);triamine compounds (Japanese Unexamined Patent Application PublicationNo. 5-239455); bisdipyridylaminobiphenyl (Japanese Unexamined PatentApplication Publication No. 5-320634); N,N,N-triphenylamine derivatives(Japanese Unexamined Patent Application Publication No. 6-1972);aromatic diamines having phenoxazine structures (Japanese UnexaminedPatent Application Publication No. 7-138562);diaminophenylphenanthridine derivatives (Japanese Unexamined PatentApplication Publication No. 7-252474); hydrazone compounds (JapaneseUnexamined Patent Application Publication No. 2-311591); silazanecompounds (U.S. Pat. No. 4,950,950); silanamine derivatives (JapaneseUnexamined Patent Application Publication No. 6-49079); phosphaminederivatives (Japanese Unexamined Patent Application Publication No.6-25659); and quinacridone compounds. Where necessary, each of thesearomatic amine compounds may be used in combination.

Preferred examples of phthalocyanine derivatives or porphyrinderivatives usable as the hole-transporting compound in the holeinjection layer include porphyrin,5,10,15,20-tetraphenyl-21H,23H-porphyrin,5,10,15,20-tetraphenyl-21H,23H-porphyrin cobalt(II),5,10,15,20-tetraphenyl-21H,23H-porphyrin copper(II),5,10,15,20-tetraphenyl-21H,23H-porphyrin zinc(II),5,10,15,20-tetraphenyl-21H,23H-porphyrin vanadium(IV) oxide,5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin, copper(II)29H,31H-phthalocyanine, zinc(II) phthalocyanine, titaniumphthalocyanine, magnesium phthalocyanine oxide, lead phthalocyanine,copper(II) phthalocyanine, and4,4′,4″,4′″-tetraaza-29H,31H-phthalocyanine.

Preferred examples of oligothiophene derivatives usable as thehole-transporting compound in the hole injection layer includeα-terthiophene and derivatives thereof, α-sexithiophene and derivativesthereof, and oligothiophene derivatives each containing naphthalene ring(Japanese Unexamined Patent Application Publication No. 6-256341).

Preferred examples of polythiophene derivatives usable as thehole-transporting compound in the present invention includepoly(3,4-ethylenedioxythiophene)s (PEDOT) and poly(3-hexylthiophene)s.

The molecular weights of these hole-transporting compounds, except forpolymeric compounds (polymerized compounds having a series of repeatingunits), are each generally 9000 or less, preferably 5000 or less, andare generally 200 or more, and preferably 400 or more. Ahole-transporting compound having an excessively high molecular weightmay be difficult to synthesize and purify. In contrast, ahole-transporting compound having an excessively low molecular weightmay have poor heat resistance.

The material for the hole injection layer may contain each of suchhole-transporting compounds alone or in combination. When the materialcontains two or more different hole-transporting compounds, one or morepolymeric aromatic tertiary amine compounds and one or more otherhole-transporting compounds are preferably used in combination.

Electron-Accepting Compound

Preferred as the electron-accepting compound are compounds havingoxidizing power and capability of accepting one electron from thehole-transporting compound. More specifically, compounds having anelectron affinity of 4 eV or more are preferred, of which compoundshaving an electron affinity of 5 eV or more are more preferred.

Examples of such compounds include onium salts substituted with organicgroup(s), such as 4-isopropyl-4′-methyldiphenyliodoniumtetrakis(pentafluorophenyl)borate; high-valence inorganic compounds suchas iron(III) chloride (Japanese Unexamined Patent ApplicationPublication No. 11-251067) and ammonium peroxodisulfate; cyano compoundssuch as tetracyanoethylene; aromatic boron compounds such astris(pentafluorophenyl)borane (Japanese Unexamined Patent ApplicationPublication No. 2003-31365); fullerene derivatives; and iodine.

Of these compounds, onium salts substituted with organic group(s), andhigh-valence inorganic compounds are preferred for their high oxidizingpower, and onium salts substituted with organic group(s), cyanocompounds, and aromatic boron compounds are preferred for theirsolubility in various solvents and applicability to wet coating.

Specific examples and preferred examples of such onium salts substitutedwith organic group(s), cyano compounds, and aromatic boron compounds aspreferred electron-accepting compounds include, but are not limited to,those described in PCT International Publication Number WO 2005/089024.

Cation Radical Compound

The “cation radical compound” refers to an ion compound containing acation radical and a counter anion, in which the cation radical is achemical species corresponding to a hole-transporting compound exceptfor removing one electron therefrom. However, when the cation radical isderived from a hole-transporting polymeric compound, the cation radicalhas a structure corresponding to the polymeric compound, except forremoving one electron from its repeating unit.

The cation radical is preferably a chemical species corresponding to oneof the above-listed hole-transporting compounds, except for removing oneelectron therefrom, and is more preferably one of the above-listedpreferred hole-transporting compounds, except for removing one electrontherefrom. This is because these cation radicals provide furthersatisfactory non-crystallinity, transmittance to visible light, heatresistance, and solubility.

Such a cation radical compound can be formed by mixing thehole-transporting compound and the electron-accepting compound.Specifically, by mixing the hole-transporting compound and theelectron-accepting compound, an electron travels from thehole-transporting compound to the electron-accepting compound to therebyyield a cation radical compound containing a cation radical of thehole-transporting compound, and a counter anion.

Cation radical compounds derived from polymeric compounds, such aspoly(ethylene dioxythiophene) doped with polystyrene sulfonic acid(PEDOT/PSS) (Adv. Mater., 2000, vol. 12, p. 481) and emeraldinehydrochloride (J. Phys. Chem., 1990, vol. 94, p. 7716) can also beformed through oxidative polymerization (dehydrogenativepolymerization). Namely, they can be formed by chemically orelectrochemically oxidizing one or more monomers typically with aperoxodisulfate in an acidic solution. In the oxidative polymerization(dehydrogenative polymerization), the monomer is polymerized and acation radical corresponding to the polymer, except for removing oneelectron from its repeating unit, is formed as a result of oxidation. Ananion derived from the acidic solution serves as a counter anion withrespect to the cation radical.

The hole injection layer 3 is formed on or above the anode 2 through wetfilm-formation or vacuum deposition.

Indium thin oxide (ITO) generally used as the anode 2 has a surfaceroughness (Ra) of about 10 nm, often has local projections, and isthereby liable to cause bridging faults. The hole injection layer 3 isadvantageously formed on or above the anode 2 through wet film-formationrather than vacuum deposition, so as to reduce defects of the devicecaused by the unevenness of the anode surface.

When the hole injection layer 3 is formed through wet film-formation,the layer may be formed by dissolving predetermined amounts of one ormore of the respective materials including the hole-transportingcompounds, the electron-accepting compounds, and the cation radicalcompounds, and where necessary a coatability improver and a binder resinthat does not act as a charge trap, in a solvent to yield a coatingsolution, applying the coating solution to the anode through wetfilm-formation, and drying the applied film. Examples of processes forthe wet film-formation include spin coating, spray coating, dip coating,die coating, flexographic printing, screen printing, and an ink-jetprocess.

Solvents for use in the formation of the layer through wetfilm-formation are not specifically limited in their types, as long asthey are solvents that can dissolve the respective materials includingthe hole-transporting compounds, the electron-accepting compounds, andthe cation radical compounds therein. They preferably contain neitherdeactivating substances nor substances forming such deactivatingsubstances. The deactivating substances herein are substances that maydeactivate the respective materials for the hole injection layer,including the hole-transporting compounds, the electron-acceptingcompounds, and the cation radical compounds.

Examples of preferred solvents satisfying these conditions include ethersolvents and ester solvents. Specific examples of ether solvents includealiphatic ethers such as ethylene glycol dimethyl ether, ethylene glycoldiethyl ether, and propylene glycol-1-monomethyl ether acetate (PGMEA);and aromatic ethers such as 1,2-dimethoxybenzene, 1,3-dimethoxybenzene,anisole, phenetole, 2-methoxytoluene, 3-methoxytoluene,4-methoxytoluene, 2,3-dimethylanisole, and 2,4-dimethylanisole. Specificexamples of ester solvents include aliphatic esters such as ethylacetate, n-butyl acetate, ethyl lactate, and n-butyl lactate; andaromatic esters such as phenyl acetate, phenyl propionate, methylbenzoate, ethyl benzoate, propyl benzoate, and n-butyl benzoate. Each ofthese can be used alone or used in any combinations and proportions.

In addition to the ether solvents and ester solvents, solvents usableherein also include aromatic hydrocarbon solvents such as benzene,toluene, and xylenes; amide solvents such as N,N-dimethylformamide andN,N-dimethylacetamide; and dimethyl sulfoxide. Each of these can be usedalone or used in any combinations and proportions. It is acceptable touse one or more of these solvents in combination with one or more of theether solvents and ester solvents. In particular, aromatic hydrocarbonsolvents, such as benzene, toluene, and xylenes, are preferably used incombination with one or more of the ether solvents and ester solvents,because they have low capability of dissolving electron-acceptingcompounds and cation radical compounds.

Solvents containing deactivating substances that may deactivate therespective materials for the hole injection layer including thehole-transporting compounds, the electron-accepting compounds, and thecation radical compounds, or solvents containing substances forming suchdeactivating substances include aldehyde solvents such as benzaldehyde;and ketone solvents having hydrogen atom at the alpha position, such asmethylethyl ketone, cyclohexanone, and acetophenone. These aldehydesolvents and ketone solvents are undesirable, because they may causecondensation reaction between solvent molecules or may react with therespective materials including the hole-transporting compounds,electron-accepting compounds, and cation radical compounds to yieldimpurities.

The concentration of the solvent in the coating solution is generally 10percent by weight or more, preferably 30 percent by weight or more, morepreferably 50 percent by weight or more, and is generally 99.999 percentby weight or less, preferably 99.99 percent by weight or less, andfurther preferably 99.9 percent by weight or less. When two or moredifferent solvents are used as the solvent, the total concentration ofthese solvents may be set within this range.

When the hole injection layer is formed through vacuum deposition, thelayer may be formed in the following manner. One of the respectivematerials including the hole-transporting compounds, theelectron-accepting compounds, or the cation radical compounds, when usedalone, is placed in a crucible disposed in a vacuum chamber, the vacuumchamber is evacuated using a proper vacuum pump to a pressure of about10⁻⁴ Pa, the crucible is heated to vaporize the material to thereby forma hole injection layer on the anode on a substrate placed facing thecrucible, while controlling the amount of evaporation. When two or moreof the materials are used, the above procedure is repeated, except thatthe materials are placed in different crucibles disposed in a vacuumchamber, respectively, the crucibles are heated respectively, and theamounts of the evaporated materials are controlled independently. Whentwo or more of the materials are used, the hole injection layer can alsobe formed by placing a mixture of these materials in a crucible, andheating the crucible to evaporate the mixture.

The thickness of the hole injection layer 3 which may be formed in theabove manner is generally 5 nm or more, preferably 10 nm or more, and isgenerally 1000 nm or less, and preferably 500 nm or less.

<Organic Light Emitting Layer>

An organic light emitting layer 4 is arranged on the hole injectionlayer 3. The organic light emitting layer 4 is a layer formed by usingthe composition for an organic electroluminescent device according tothe present invention containing a luminescent material, a chargetransporting material, and a solvent. The organic light emitting layercan mainly emit light when strongly excited in a space between energizedelectrodes. The excitation is caused by recombination of holes injectedfrom the anode 2 via the hole injection layer 3 with electrons injectedfrom the cathode 6 via the electron injection layer 5. The organic lightemitting layer 4 may further contain any other materials and components,within ranges not adversely affecting the performance obtained accordingto the present invention. A device according to the present invention ispreferably prepared using a method including the step of forming theorganic light emitting layer through wet film-formation using thecomposition. The wet film-formation herein is as described in the thinfilm for an organic electroluminescent device according to the presentinvention.

Provided that the same material is used, an organic electroluminescentdevice generally operates at a decreasing drive voltage with adecreasing thickness of a layer between the electrodes, because theeffective electric field increases and thereby the injected currentincreases with a decreasing thickness. Accordingly, the organicelectroluminescent device operates at a decreasing drive voltage with adecreasing thickness of layers between the electrodes. The totalthickness of the layers, however, should be a certain level or more,because an excessively small total thickness may cause short circuit dueto projections typically caused by the electrodes made typically of ITO.

When a device according to the present invention further includes a holeinjection layer and an electron injection layer in addition to theorganic light emitting layer, the total thickness of the organic lightemitting layer 4 and other organic layers such as the hole injectionlayer 3 and the electron injection layer 5 is generally 30 nm or more,preferably 50 nm or more, and further preferably 100 nm or more, and isgenerally 1000 nm or less, preferably 500 nm or less, and furtherpreferably 300 nm or less. When the hole injection layer 3 and/or theelectron injection layer 5 other than the organic light emitting layer 4has a high electroconductivity, the amount of charges to be injected tothe organic light emitting layer 4 increases. In this case, the drivevoltage can be reduced while maintaining the total thickness to acertain level by increasing the thickness of, for example, the holeinjection layer 3 and decreasing the thickness of the organic lightemitting layer 4.

Accordingly, the thickness of the organic light emitting layer 4 in thiscase is generally 10 nm or more, preferably 20 nm or more, and isgenerally 300 nm or less, and preferably 200 nm or less. When a deviceaccording to the present invention includes the organic light emittinglayer alone between the anode and the cathode, the thickness of theorganic light emitting layer 4 is generally 30 nm or more, preferably 50nm or more, and is generally 500 nm or less, preferably 300 nm or less.

A thin film as the organic light emitting layer 4 is formed according tothe wet film-formation process described in the thin film for an organicelectroluminescent device according to the present invention.

<Electron Injection Layer>

The electron injection layer 5 functions to inject electrons injectedfrom the cathode 6 into the organic light emitting layer 4 efficiently.To conduct electron injection efficiently, materials for constitutingthe electron injection layer 5 are preferably metals having low workfunctions, including alkali metals such as sodium and cesium; andalkaline earth metals such as barium and calcium. The thickness of thislayer is preferably 0.1 to 5 nm.

Further, in order to improve efficiency of the device, it is also aneffective technique to arrange an extremely thin insulating filmtypically of LiF, MgF₂, or Li₂O at the interface between the cathode 6and the light-emitting layer 4 or the after-mentioned electron transportlayer 8 (Appl. Phys. Lett., vol. 70, p. 152, 1997; Japanese UnexaminedPatent Application Publication No. 10-74586; IEEE Trans. Electron.Devices, vol. 44, p. 1245, 1997; and SID 04 Digest, p. 154).

It is preferred to dope an organic electron transporting material withan alkali metal such as sodium, potassium, cesium, lithium, or rubidium(described typically in Japanese Unexamined Patent ApplicationPublications No. 10-270171, No. 2002-100478, and No. 2002-100482),because this serves to improve the electron injection/transportingability and to provide excellent film quality. The organic electrontransporting material is typified by nitrogen-containing heterocycliccompounds such as bathophenanthroline; and metal complexes such asaluminum 8-hydroxyquinoline complex. The thickness of this layer isgenerally 5 nm or more, preferably 10 nm or more, and is generally 200nm or less, and preferably 100 nm or less.

The electron injection layer 5 may be formed by forming a film on theorganic light emitting layer 4 by a coating process as in the organiclight emitting layer 4 or by vacuum deposition. When vacuum depositionis employed, the electron injection layer may be formed by placing anevaporation source in a crucible or metal boat disposed in a vacuumchamber, evacuating the vacuum chamber to a pressure of about 10⁻⁴ Pausing a proper vacuum pump, heating the crucible or metal boat toevaporate the evaporation source, and thereby forming a film as theelectron injection layer on a substrate placed facing the crucible ormetal boat.

The evaporation of the alkaline metal is usually carried out using analkaline metal dispenser containing an alkaline metal salt of chromicacid and a reducing agent packed in a Ni—Cr alloy (nichrome). By heatingthis dispenser in a vacuum chamber, the alkaline metal salt of chromicacid is reduced so that the alkaline metal is evaporated. When anorganic electron transporting material and an alkali metal areco-evaporated, the organic electron transporting material is put in acrucible placed in the vacuum chamber. The vacuum chamber is thenevacuated to a pressure of about 10⁻⁴ Torr by a proper vacuum pump. Thecrucible and the dispenser are then simultaneously heated to evaporatethe materials so that an electron injection/transport layer is formed ona substrate disposed facing the crucible and the dispenser.

In this case, the materials are co-deposited homogenously in a thicknessdirection of the electron injection layer. However, there may bedistribution in concentrations of the materials in a thicknessdirection.

<Cathode>

The cathode 6 serves to inject electrons into the organic light emittinglayer 4, or a layer arranged between the cathode and the organic lightemitting layer, such as the electron injection layer 5. As materials forthe cathode 6, those materials which are used for the anode 2 may beemployed but, in order to inject electrons highly efficiently, metalshaving low work functions are preferred. Thus, suitable metals such astin, magnesium, indium, calcium, aluminum and silver or alloys thereofare used. Specific examples of the cathode include electrodes of alloyshaving a low work function, such as a magnesium-silver alloy, amagnesium-indium alloy and a aluminum-lithium alloy. The thickness ofthe cathode 6 is generally as with that of the anode 2. A metal layerhaving a high work function and stable in the atmosphere may be arrangedon the cathode in order to protect the cathode formed from such a metalhaving a low work function. This improves the stability of the device.For this purpose, metals such as aluminum, silver, copper, nickel,chromium, gold, and platinum are used.

<Other Constitutive Layers>

While there has been mainly described a device having the layerconfiguration shown in FIG. 2, an organic electroluminescent deviceaccording to the present invention may further include any other layersbetween the anode 2 and the organic light emitting layer 4 and betweenthe cathode 6 and the organic light emitting layer 4 in addition to theabove-illustrated layers, as long as not adversely affecting theperformance of the device. Any layer between the cathode 6 and the anode2, except for the organic light emitting layer 4, may be omitted.

An example of the layers which the device may further include is anelectron blocking layer 7 arranged between the hole injection layer 3and the organic light emitting layer 4 (refer to FIGS. 3, 4, and 5). Theelectron blocking layer 7 serves to block electrons having migrated fromthe organic light emitting layer 4 from reaching the hole injectionlayer 3, to thereby increase the recombination probability betweenelectrons and holes in the organic light emitting layer 4, and toconfine resulting exitons within the light emitting layer 4. It alsoserves to transport holes injected from the hole injection layer 3toward the organic light emitting layer 4 efficiently. This layer isparticularly effective when a phosphorescent material or a blue-emittingmaterial is used as a luminescent material. Properties required for theelectron blocking layer 7 are high hole transporting ability, a largeenergy gap (difference between the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital (LUMO)), and a highexcited triplet level (T1). In addition, the electron blocking layer 7should be applicable to wet film-formation, because the organic lightemitting layer 4 in a device according to the present invention isformed through wet film-formation, and the device is thereby easilymanufactured. Examples of materials for the electron blocking layer 7include copolymers of dioctylfluorene and triphenylamine, typified byF8-TFB (described in PCT International Publication Number WO2004/084260).

The layers which the device may further have also include an electrontransport layer 8. The electron transport layer 8 is arranged betweenthe organic light emitting layer 4 and the electron injection layer 5 inorder to further improve the luminous efficiency of the device (FIGS. 4,5, 6, and 7).

The electron transport layer 8 is formed from a compound which canefficiently transport electrons injected from the cathode 6 toward theorganic light emitting layer 4 between the energized electrodes.Electron transporting compounds for use in the electron transport layer8 must be compounds that efficiently inject electrons from the cathode 6or the electron injection layer 5 and have high electron mobility tothereby efficiently transport the injected electrons.

Examples of materials satisfying such conditions include metal complexessuch as aluminum complex of 8-hydroxyquinoline (Japanese UnexaminedPatent Application Publication No. 59-194393); metal complexes of10-hydroxybenzo[h]quinoline; oxadiazole derivatives; distyrylbiphenylderivatives; silole derivatives; metal complexes of 3- or5-hydroxyflavone; metal complexes of benzoxazole; metal complexes ofbenzothiazole; trisbenzimidazolylbenzene (U.S. Pat. No. 5,645,948);quinoxaline compounds (Japanese Unexamined Patent ApplicationPublication No. 6-207169); phenanthroline derivatives (JapaneseUnexamined Patent Application Publication No. 5-331459);2-t-butyl-9,10-N,N′-dicyanoanthraquinonediimine; n-type hydrogenatedamorphous silicon carbide; n-type zinc sulfide; and n-type zincselenide.

The lower limit of the thickness of the electron transport layer 8 isgenerally about 1 nm, and preferably about 5 nm, and its upper limit isgenerally about 300 nm, and preferably about 100 nm.

The electron transport layer 8 may be formed on the organic lightemitting layer 4 by coating or vacuum deposition in the same manner aswith the hole injection layer 3, but this layer is generally formed byvacuum deposition.

It is also effective to provide a hole blocking layer 9 (refer to FIGS.5 and 7), for the same purpose as with the electron blocking layer 7.The hole blocking layer 9 is arranged on the organic light emittinglayer 4 at an interface of the organic light emitting layer 4 facing thecathode 6. This layer is formed by a compound which serves to preventholes migrating form the anode 2 from reaching the cathode 6 and canefficiently transport electrons injected from the cathode 6 toward theorganic light emitting layer 4. Required properties for the materialconstituting the hole blocking layer 9 include a high electron mobilityand a low hole mobility, a large energy gap (difference between thehighest occupied molecular orbital (HOMO) and the lowest unoccupiedmolecular orbital (LUMO)), and a high excited triplet level (T1). Thehole blocking layer 9 has the function of confining holes and electronswithin the organic light emitting layer 4 to thereby improve theluminous efficiency.

Examples of materials for the hole blocking layer satisfying theseconditions include mixed ligand complexes such asbis(2-methyl-8-quinolinolato)(phenolato)aluminum andbis(2-methyl-8-quinolinolato)(triphenylsilanolato)aluminum; metalcomplexes such asbis(2-methyl-8-quinolato)aluminum-μ-oxo-bis-(2-methyl-8-quinolylato)aluminumbinuclear metal complex; styryl compounds such as distyrylbiphenylderivatives (Japanese Unexamined Patent Application Publication No.11-242996); triazole derivatives such as3-(4-biphenylyl)-4-phenyl-5(4-tert-butylphenyl)-1,2,4-triazole (JapaneseUnexamined Patent Application Publication No. 7-41759); andphenanthroline derivatives such as bathocupuroine (Japanese UnexaminedPatent Application Publication No. 10-79297).

Preferred hole blocking materials further include compounds having atleast one pyridine ring substituted on the 2-, 4-, and/or 6-position,represented by following General Formula (12):

In General Formula (12), R⁵¹, R⁵², and R⁵³ each independently representhydrogen atom or any substituent; linkage group G represents a linkagegroup having a valency of “m”, where the linkage group G is directlybound to the pyridine ring at any one of the 2-, 3-, 4-, 5-, and6-positions; and “m” represents an integer of 1 to 8.

Specific examples of the compounds having at least one pyridine ringsubstituted at 2-, 4-, and/or 6-position, represented by the structuralformula are illustrated below, which, however, are not limitative atall.

The thickness of the hole blocking layer 9 is generally 0.3 nm or more,preferably 0.5 nm or more, and is generally 100 nm or less, andpreferably 50 nm or less. The hole blocking layer 9 can be formed in thesame manner as with the hole injection layer 3, but it is generallyformed by vacuum deposition.

The electron transport layer 8 and the hole blocking layer 9 may bearranged as appropriate according to necessity. A device may have, forexample, 1) the electron transport layer alone, 2) the hole blockinglayer alone, 3) a multilayer of the hole blocking layer and the electrontransport layer, or 4) none of the two layers.

A reverse layer structure to that in FIG. 2 is also possible. In thereversed structure, on a substrate 1, there are sequentially arranged acathode 6, an electron injection layer 5, an organic light emittinglayer 4, a hole injection layer 3, and an anode 2 in this order. As isdescribed above, an organic electroluminescent device according to thepresent invention may be arranged between two substrates, at least oneof which is highly transparent. Likewise, reverse layer structures tothose shown in FIGS. 3 to 7, respectively, are also possible.

It is also possible to employ a layer structure in which a plurality ofthe layer structures shown in FIGS. 2 to 7 are stacked (a structureincluding a plurality of the light-emitting units as stacked). In thiscase, V₂O₅, for example, is preferably used as a charge generating layer(CGL) instead of the interface layers (when ITO and aluminum (Al) areused as the anode and the cathode, respectively, the two layers of theanode and the cathode) between the units (light-emitting units). Thisserves to reduce barrier between the units, thus being more preferred inview of luminous efficiency and drive voltage.

The present invention can be applied to any of structures of organicluminescent devices, such as a structure in which the organicelectroluminescent device includes a single device, a structure whichincludes devices arranged in an array form, and a structure wherein theanode and the cathode are arranged in an X-Y matrix pattern.

An organic electroluminescent device according to the present inventionuses a composition for an organic electroluminescent device according tothe present invention which contains a luminescent material and a chargetransporting material having a specific relationship inoxidation/reduction potentials, and a solvent. The device can thereby beeasily manufactured, has a high luminous efficiency, and showssignificantly improved drive stability. The device can thereby exhibitexcellent performance when applied to large-area display devices orlightning.

EXAMPLES

Next, the present invention will be illustrated in further detail withreference to a measurement example, several examples and comparativeexamples below, which, however, are not limitative at all, as long asnot exceeding the scope and the spirit of the present invention.

Measurement Example 1 Determination of Oxidation/Reduction Potentials ofCompounds

The oxidation/reduction potentials of following Compounds T1 to T4 andD4 were determined by cyclic voltammetry.

A series of sample solutions to be measured was prepared by dissolvingtetrabutylammonium perchlorate in each analysis solvent in Table 1 toyield 0.1 mol/L solutions and further dissolving one of the compounds inthe solutions to a concentration of 1 mmol/L. The measurement wasconducted at a sweep rate of 100 mV/s using glassy carbon (supplied fromBAS Inc.) as a working electrode, a platinum wire as a counterelectrode, and a silver wire as a reference electrode. Theoxidation/reduction potentials were determined by usingferrocene/ferrocenium (Fc/Fc⁺) as an internal standard and convertingthe measured potentials of samples into potentials versus a saturatedcalomel electrode (SCE), provided that the internal standard has apotential of +0.41 V vs. SCE. The determined first oxidation potentialsand first reduction potentials of the compounds are shown in Table 1.

TABLE 1 Oxidation Potential Reduction Potential Compound [V vs. SCE] [Vvs. SCE] Analysis Solvent T1 +1.34 −2.10 1:1 by volume (25° C.) mixtureof acetonitrile and tetrahydrofuran T2 +1.76 −2.03 Oxidation potential:methylene chloride Reduction potential: acetonitrile T3 +0.99 −2.10 1:1by volume (25° C.) mixture of acetonitrile and tetrahydrofuran T4 +1.29−2.05 N,N-dimethylformamide D1 +0.72 −2.30 1:1 by volume (25° C.)mixture of acetonitrile and tetrahydrofuran

Example 1 Device Preparation 1

An indium-tin oxide (ITO) transparent electroconductive film depositedto a thickness of 150 nm on a glass substrate (supplied from SanyoVacuum Industries Co., Ltd., sputtered film) was patterned in a 2-mmwidth stripe pattern using a common photolithography technique andetching with hydrochloric acid-iron chloride solution thereby forming ananode. The patterned ITO substrate was rinsed by sequentially carryingout ultrasonic cleaning in an aqueous surfactant solution and rinsingwith pure water, followed by drying in dried nitrogen gas, and UV/ozonecleaning. In addition, a composition for an organic electroluminescentdevice was prepared by mixing 90 mg of the compound (T1), 90 mg of thecompound (T2), and 9 mg of the compound (D1), each represented by thestructural formula, and 2.8 g of chlorobenzene as a solvent, andremoving insoluble matter by filtration through a PTFE membrane filterhaving a pore size of 0.2 μm. The composition was applied to the ITOsubstrate by spin coating under the following conditions to thereby forma uniform thin film having a thickness of 160 nm.

Revolution number of spinner: 1500 rpm

Revolution time of spinner: 30 seconds

Spinning atmosphere: in the atmosphere at a temperature of 23° C. andrelative humidity of 30%

Drying condition: drying by heating in an oven at 140° C. for 15 minutes

When Compound D1 has a first reduction potential of E_(D1) ⁻ [V vs. SCE]and a first oxidation potential of E_(D1) ⁺ [V vs. SCE], and

Compound T1 has a first reduction potential of E_(T1) ⁻ [V vs. SCE] anda first oxidation potential of E_(T1) ⁺ [V vs. SCE], the first oxidationpotentials and first reduction potentials in this composition satisfythe following condition:

E _(D1) ⁻(−2.30)+0.1<E _(T1) ⁻(−2.03)<E _(D1) ⁺(+0.72)<E _(T1)⁺(+1.34)−0.1

Next, a 2-mm width striped shadow mask as a mask for the vacuumdeposition of a cathode was brought into intimate contact with thesubstrate bearing the coated film perpendicular to the ITO stripe of theanode, and the device was then placed in a vacuum deposition apparatus.After roughly evacuating the apparatus using an oil rotary pump, theapparatus was evacuated to a vacuum degree of 3×10⁻⁴ Pa or less. As acathode, an alloy electrode of magnesium and silver was deposited invacuo to a thickness of 110 nm through co-evaporation, in whichmagnesium and silver were placed in different molybdenum boats andheated simultaneously. The vacuum deposition of magnesium was conductedat a deposition rate of 0.4 to 0.5 nm per second and a degree of vacuumof 5×10⁻⁴ Pa, and the atomic ratio of magnesium to silver was set at10:1.4. The temperature of the substrate upon vacuum deposition of thecathode was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared.

The light emitting properties of the device are shown in Table 2.

This device emitted green light with a luminance of 30 cd/m² uponapplication of a voltage of 55 V at a flowing current density of 120mA/cm² and a luminous efficiency of 0.1 lm/W. The electro-emissionspectrum of the device is shown in FIG. 8. The dimensions of theemission spectrum demonstrate that the light is emitted from CompoundD1.

Example 2 Device Preparation 2

A composition for an organic electroluminescent device was prepared bymixing 90 mg of the compound (T3), 90 mg of the compound (T4), and 9 mgof the compound (D1), each represented by the structural formula, and2.8 g of o-dichlorobenzene as a solvent, and removing insoluble matterby filtration through a PTFE membrane filter having a pore size of 0.2μm. In addition, an ITO substrate was patterned and rinsed in the samemanner as with Example 1. The composition was applied to the resultingITO substrate by spin coating under the following conditions to therebyform a uniform thin film having a thickness of 160 nm.

Revolution number of spinner: 1500 rpm

Revolution time of spinner: 30 seconds

Spinning atmosphere: spinning was conducted in the atmosphere at atemperature of 23° C. and relative humidity of 30%

Drying condition: drying by heating on a hot plate at 80° C. for 1minutes and further drying by heating in an oven at 140° C. for 15minutes

When Compound D1 has a first reduction potential of E_(D1) ⁻ [V vs. SCE]and a first oxidation potential of E_(D1) ⁺ [V vs. SCE], and

Compound T3 has a first reduction potential of E_(T3) ⁻ [V vs. SCE] anda first oxidation potential of E_(T3) ⁺ [V vs. SCE], the first oxidationpotentials and first reduction potentials in this composition satisfythe following condition:

E _(D1) ⁻(−2.30)+0.1<E _(T3) ⁻(−2.05)<E _(D1) ⁺(+0.72)<E _(T3)⁺(+0.99)−0.1

Next, the substrate bearing the coated film was placed in a vacuumdeposition apparatus, and the apparatus was evacuated in the same manneras with Example 1. A film of sodium was applied by vapor deposition to athickness of 0.5 nm. The vapor deposition of sodium was conducted byheating a sodium dispenser (supplied from SAES Getters) containingsodium chromate. The vapor deposition was conducted at an averagedeposition rate of 0.01 nm per second and a degree of vacuum of 8×10⁻⁵Pa. Subsequently, aluminum was deposited using a molybdenum boat at adeposition rate of 0.4 to 0.6 nm per second and a degree of vacuum of5×10⁻⁴ Pa to yield an aluminum film 80 nm thick. The temperature of thesubstrate upon vapor deposition of sodium and aluminum was kept to roomtemperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared.

The light emitting properties of this device, namely, the emissionluminance (in unit of cd/m²) at a flowing current density of 250 mA/cm²,the luminous efficiency (in unit of lm/W) at an emission luminance of100 cd/m², and the drive voltage (in unit of V) are shown in Table 2.

The results in Table 2 demonstrate that a device that emits light with ahigh luminance was obtained by using a multilayer electrode of sodiumand aluminum as the cathode.

Example 3 Device Preparation 3

Initially, an ITO substrate was patterned and rinsed in the same manneras with Example 2 and was immersed in a solution for five minutes. Thesolution was a 5 mM solution of the compound (ST1) represented by thefollowing structural formula in dichloromethane. The substrate was thentaken out from the solution, rinsed with dichloromethane for one minute,and was dried using a nitrogen blow. Thus, surface treatment of the ITOanode was conducted.

A composition for an organic electroluminescent device was prepared bymixing 60 mg of the compound (T3), 10 mg of the compound (T4), 4 mg ofthe compound (D1), and 2 g of o-dichlorobenzene as a solvent, andremoving insoluble matter by filtration through a PTFE membrane filterhaving a pore size of 0.2 μm. The composition was applied to the surfacetreated ITO substrate by spin coating under the condition as withExample 2 to form a uniform thin film having a thickness of 160 nm.

Next, sodium was deposited on the substrate bearing the coated film toform a film 0.5 nm thick, and aluminum was deposited thereon to form afilm 80 nm thick in the same manner as with Example 2.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared.

The light emitting properties of this device, namely, the emissionluminance (in unit of cd/m²) at a flowing current density of 250 mA/cm²,the luminous efficiency (in unit of lm/W) at an emission luminance of100 cd/m², and the drive voltage (in unit of V), are shown in Table 2.

The results in Table 2 demonstrate that a device that emits light with afurther higher luminance was obtained by subjecting the ITO anode tosurface treatment.

TABLE 2 Measuring Condition Flowing Current Density Luminance250[mA/cm²] 100 [cd/m²] Measured Data Luminance [cd/m²] LuminousEfficiency [lm/W] Drive Voltage [V] Example 1    30¹⁾   0.1²⁾ 55³⁾ Example 2 2050 0.2 12.3  Example 3 3040 0.4 9.2 ¹⁾The luminance of thedevice prepared according to Example 1 was measured at a flowing currentdensity of 120 mA/cm². ²⁾The luminous efficiency of the device preparedaccording to Example 1 was measured at a luminance of 30 cd/m². ³⁾Thedrive voltage of the device prepared according to Example 1 was measuredat a luminance of 30 cd/m².

Example 4 Device Preparation 4

An organic electroluminescent device having the structure shown in FIG.6 was prepared in the following manner.

An indium-tin oxide (ITO) transparent electroconductive film depositedto a thickness of 150 nm on a glass substrate 1 (sputtered film; sheetresistance: 15Ω) was patterned in a 2-mm width striped pattern using acommon photolithography technique and etching with hydrochloric acid,thereby forming an anode 2. The patterned ITO substrate was rinsed bysequentially carrying out ultrasonic cleaning in acetone, rinsing withpure water, and rinsed by sequentially carrying out ultrasonic cleaningin isopropyl alcohol, followed by drying in a nitrogen blow and UV/ozonecleaning.

Next, a hole injection layer 3 was formed by wet coating in thefollowing manner. As materials for the hole injection layer 3, apolymeric compound (PB-1) having a weight-average molecular weight of26500 and a number-average molecular weight of 12000 and containing anaromatic amino group of the following structural formula, and anelectron-acceptor (A-2) of the following structural formula were appliedby spin coating under the following conditions.

<Conditions of Spin Coating>

Solvent: anisole

Concentrations in coating composition: 2.0 percent by weight of PB-1,and

-   -   0.4 percent by weight of A-2

Revolution number of spinner: 2000 rpm

Revolution time of spinner: 30 seconds

Drying condition: drying at 230° C. for 5.5 hours

A uniform thin film 30 nm thick was formed by the spin coating.

Subsequently, an organic light emitting layer 4 was formed by wetcoating in the following manner. A composition for an organicelectroluminescent device was prepared by dissolving the compounds (T5)and (D2) as materials for the light emitting layer 4 in concentrationsin a solvent shown below. The composition was applied by spin coatingunder the following conditions, to thereby yield the organic lightemitting layer 4.

<Conditions of Spin Coating>

Solvent: xylene

Concentrations in coating composition: 2.5 percent by weight of T5

-   -   0.13 percent by weight of D2

Revolution number of spinner: 1500 rpm

Revolution time of spinner: 30 seconds

Drying condition: drying at 130° C. under reduced pressure for 60minutes

A uniform thin film 45 nm thick was formed by the spin coating.

Next, following aluminum 8-hydroxyquinoline complex (ET-1) was depositedas an electron transport layer 8. The temperature of the crucible ofaluminum 8-hydroxyquinoline complex in this procedure was controlledwithin the range of from 321° C. to 311° C. The vacuum deposition wasconducted at a degree of vacuum of 1.3 to 1.5×10⁻⁴ Pa (about 1.1 to1.0×10⁻⁶ Torr) and a deposition rate of 0.08 to 0.16 nm per second toyield a film 30 nm thick.

The temperature of the substrate upon vacuum deposition of the electrontransport layer 8 was kept to room temperature.

The device which had been subjected to vacuum deposition up to theelectron transport layer 8 was once taken out of the vacuum depositionapparatus into the atmosphere. A 2-mm width striped shadow mask as amask for vacuum deposition of a cathode was brought into intimatecontact with the device perpendicularly to the ITO stripe of the anode2, and the device was placed in another vacuum deposition apparatus. Theapparatus was evacuated to a degree of vacuum of 1.8×10⁻⁶ Torr (about2.4×10⁻⁴ Pa) or less in the same manner as with the organic layers.

As an electron injection layer 5, lithium fluoride (LiF) was depositedto a thickness of 0.5 nm on the electron transport layer 8. The vacuumdeposition was conducted at a deposition rate of 0.01 to 0.06 nm persecond and a degree of vacuum of 2.0×10⁻⁶ Torr (about 2.6×10⁻⁴ Pa) usinga molybdenum boat.

Next, aluminum was heated in the same manner using a molybdenum boat andwas deposited at a deposition rate of 0.1 to 0.3 nm per second and adegree of vacuum of 3.0 to 6.8×10⁻⁶ Torr (about 4.0 to 9.0×10⁻⁴ Pa) toyield an aluminum layer 80 nm thick. A cathode 6 was thus completed.

The temperature of the substrate upon vacuum deposition of thetwo-layered cathode 6 was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. The maximal wavelength inemission spectrum of the device was 515 nm, which was identified asbeing from the iridium complex (D2). The chromaticity in terms of CIE(x, y) was (0.310, 0.626).

Example 5 Device Preparation 5

An organic electroluminescent device having the structure shown in FIG.7 was prepared in the following manner.

Film-formation up to the organic light emitting layer 4 was conducted inthe same manner as with Example 4, except that the hole injection layer3 was dried at 230° C. for three hours. Thereafter, the followingpyridine derivative (HB-1) was deposited as a hole blocking layer 9 to athickness of 5 nm. The vacuum deposition was conducted at a crucibletemperature of 230° C. to 238° C., a deposition rate of 0.07 to 0.11 nmper second, and a degree of vacuum of 1.9×10⁻⁴ Pa (about 1.4×10⁻⁶ Torr).

Next, the aluminum 8-hydroxyquinoline complex (ET-1) was deposited as anelectron transport layer 8 on the hole blocking layer 9 in the samemanner. The temperature of the crucible for the aluminum8-hydroxyquinoline complex in this procedure was controlled within therange of from 352° C. to 338° C. The vacuum deposition was conducted ata degree of vacuum of 2.0 to 1.9×10⁻⁴ Pa (about 1.5 to 1.4×10⁻⁶ Torr)and a deposition rate of 0.07 to 0.13 nm per second to yield a film 30nm thick.

The temperature of the substrate upon vacuum deposition of the holeblocking layer 9 and the electron transport layer 8 was kept to roomtemperature.

The device which had been subjected to vacuum deposition up to theelectron transport layer 8 was once taken out of the vacuum depositionapparatus into the atmosphere. A 2-mm width striped shadow mask as amask for vacuum deposition of a cathode was brought into intimatecontact with the device perpendicularly to the ITO stripe of the anode2, and the device was placed in another vacuum deposition apparatus. Theapparatus was evacuated to a degree of vacuum of 2.0×10⁻⁶ Torr (about2.6×10⁻⁴ Pa) or less in the same manner as with the organic layers.

As an electron injection layer 5, lithium fluoride (LiF) was depositedto a thickness of 0.5 nm on the electron transport layer 8. The vacuumdeposition was conducted at a deposition rate of 0.01 to 0.06 nm persecond and a degree of vacuum of 2.1×10⁻⁶ Torr (about 2.8×10⁻⁴ Pa) usinga molybdenum boat.

Next, aluminum was heated in the same manner using a molybdenum boat andwas deposited at a deposition rate of 0.2 to 0.6 nm per second and adegree of vacuum of 3.8 to 6.8×10⁻⁶ Torr (about 5.0 to 9.0×10⁻⁴ Pa) toyield an aluminum layer 80 nm thick. A cathode 6 was thus completed.

The temperature of the substrate upon vacuum deposition of thetwo-layered cathode 6 was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. The maximal wavelength inemission spectrum of the device was 515 nm, which was identified asbeing from the iridium complex (D2). The chromaticity in terms of CIE(x, y) was (0.315, 0.623).

Example 6 Device Preparation 6

An organic electroluminescent device having the structure shown in FIG.7 was prepared in the following manner.

After conducting film-formation up to the hole injection layer 3 in thesame manner as with Example 5, an organic light emitting layer 4 wasformed by wet coating in the following manner. A composition for anorganic electroluminescent device was prepared by dissolving thefollowing compounds (T6) and (D2) as materials for the light emittinglayer 4 in concentrations in a solvent mentioned below. The compositionwas applied by spin coating under the following conditions, to therebyyield the organic light emitting layer 4.

<Conditions of Spin Coating>

Solvent: xylene

Concentrations in coating composition: 3.0 percent by weight of T6

-   -   0.15 percent by weight of D2

Revolution number of spinner: 1000 rpm

Revolution time of spinner: 30 seconds

Drying condition: drying at 80° C. under reduced pressure for 60 minutes

A uniform thin film 60 nm thick was formed by the spin coating.

Next, the pyridine derivative (HB-1) was deposited as a hole blockinglayer 9 to a thickness of 5.1 nm. The vacuum deposition was conducted ata crucible temperature of 284° C. to 289° C., a deposition rate of 0.09to 0.13 nm per second, and a degree of vacuum of 2.8×10⁻⁴ Pa (about2.1×10⁻⁶ Torr).

Next, the aluminum 8-hydroxyquinoline complex (ET-1) was deposited as anelectron transport layer 8 in the same manner. The temperature of thecrucible for the aluminum 8-hydroxyquinoline complex in this procedurewas controlled within the range of from 349° C. to 340° C. The vacuumdeposition was conducted at a degree of vacuum of 2.9 to 4.3×10⁻⁴ Pa(about 2.2 to 3.2×10⁻⁶ Torr) and a deposition rate of 0.08 to 0.12 nmper second to yield a film 30 nm thick.

The temperature of the substrate upon vacuum deposition of the holeblocking layer 9 and the electron transport layer 8 was kept to roomtemperature.

The device which had been subjected to vacuum deposition up to theelectron transport layer 8 was once taken out of the vacuum depositionapparatus into the atmosphere. A 2-mm width striped shadow mask as amask for vacuum deposition of a cathode was brought into intimatecontact with the device perpendicularly to the ITO stripe of the anode2, and the device was placed in another vacuum deposition apparatus. Theapparatus was evacuated to a degree of vacuum of 2.3×10⁻⁶ Torr (about3.1×10⁻⁴ Pa) or less in the same manner as with the organic layers.

As an electron injection layer 5, lithium fluoride (LiF) was depositedto a thickness of 0.5 nm on the electron transport layer 8. The vacuumdeposition was conducted at a deposition rate of 0.005 to 0.04 nm persecond and a degree of vacuum of 2.6×10⁻⁶ Torr (about 3.42 to 3.47×10⁻⁴Pa) using a molybdenum boat.

Next, aluminum was heated in the same manner using a molybdenum boat andwas deposited at a deposition rate of 0.04 to 0.4 nm per second and adegree of vacuum of 3.5 to 7.8×10⁻⁶ Torr (about 4.6 to 10.4×10⁻⁴ Pa) toyield an aluminum layer 80 nm thick. A cathode 6 was thus completed.

The temperature of the substrate upon vacuum deposition of thetwo-layered cathode 6 was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. The maximal wavelength inemission spectrum of the device was 514 nm, which was identified asbeing from the iridium complex (D2). The chromaticity in terms of CIE(x, y) was (0.324, 0.615).

Example 7 Device Preparation 7

An organic electroluminescent device having the structure shown in FIG.7 was prepared in the following manner.

After conducting film-formation up to the hole injection layer 3 in thesame manner as with Example 5, an organic light emitting layer 4 wasformed by wet coating in the following manner. A composition for anorganic electroluminescent device was prepared by dissolving thefollowing compounds (T6) and (D3) as materials for a light emittinglayer 4 in concentrations in a solvent mentioned below. The compositionwas applied by spin coating under the following conditions, to therebyyield the organic light emitting layer 4.

<Conditions of Spin Coating>

Solvent: xylene

Concentrations in coating composition: 2.0 percent by weight of T6

-   -   0.1 percent by weight of D3

Revolution number of spinner: 1500 rpm

Revolution time of spinner: 30 seconds

Drying condition: drying at 130° C. under reduced pressure for 60minutes

A uniform thin film 60 nm thick was formed by the spin coating.

Next, the pyridine derivative (HB-1) was deposited as a hole blockinglayer 9 to a thickness of 5 nm. The vacuum deposition was conducted at acrucible temperature of 277° C. to 280° C., a deposition rate of 0.11 to0.13 nm per second, and a degree of vacuum of 2.9 to 3.2×10⁻⁴ Pa (about2.2 to 2.4×10⁻⁶ Torr).

Next, the aluminum 8-hydroxyquinoline complex (ET-1) was deposited as anelectron transport layer 8 in the same manner. The temperature of thecrucible for the aluminum 8-hydroxyquinoline complex in this procedurewas controlled within the range of from 372° C. to 362° C. The vacuumdeposition was conducted at a degree of vacuum of 3.7 to 4.3×10⁻⁴ Pa(about 2.8 to 3.2×10⁻⁶ Torr) and a deposition rate of 0.1 nm per secondto yield a film 30 nm thick.

The temperature of the substrate upon vacuum deposition of the holeblocking layer 9 and the electron transport layer 8 was kept to roomtemperature.

The device which had been subjected to vacuum deposition up to theelectron transport layer 8 was once taken out of the vacuum depositionapparatus into the atmosphere. A 2-mm width striped shadow mask as amask for vacuum deposition of a cathode was brought into intimatecontact with the device perpendicularly to the ITO stripe of the anode2, and the device was placed in another vacuum deposition apparatus. Theapparatus was evacuated to a degree of vacuum of 1.5×10⁻⁶ Torr (about3.1×10⁻⁴ Pa) or less in the same manner as with the organic layers.

As an electron injection layer 5, lithium fluoride (LiF) was depositedto a thickness of 0.5 nm on the electron transport layer 8. The vacuumdeposition was conducted at a deposition rate of 0.01 to 0.03 nm persecond and a degree of vacuum of 2.3 to 2.5×10⁻⁶ Torr (about 3.1 to3.3×10⁻⁴ Pa) using a molybdenum boat.

Next, aluminum was heated in the same manner using a molybdenum boat andwas deposited at a deposition rate of 0.3 to 0.5 nm per second and adegree of vacuum of 2.9 to 6.6×10⁻⁶ Torr (about 3.8 to 8.8×10⁻⁴ Pa) toyield an aluminum layer 80 nm thick. A cathode 6 was thus completed.

The temperature of the substrate upon vacuum deposition of thetwo-layered cathode 6 was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. The maximal wavelength inemission spectrum of the device was 513 nm, which was identified asbeing from the iridium complex (D3). The chromaticity in terms of CIE(x, y) was (0.303, 0.625).

Example 8 Device Preparation 8

An organic electroluminescent device having the structure shown in FIG.7 was prepared in the following manner.

After conducting film-formation up to the hole injection layer 3 in thesame manner as with Example 5, an organic light emitting layer 4 wasformed by wet coating in the following manner. A composition for anorganic electroluminescent device was prepared by dissolving thefollowing compounds (T7) and (D2) as materials for a light emittinglayer 4 in concentrations in a solvent mentioned below. The compositionwas applied by spin coating under the following conditions, to therebyyield the organic light emitting layer 4.

<Conditions of Spin Coating>

Solvent: 1,4-dioxane

Concentrations in coating composition: 2.0 percent by weight of T7

-   -   0.1 percent by weight of D2

Revolution number of spinner: 1500 rpm

Revolution time of spinner: 30 seconds

Drying condition: drying at 130° C. under reduced pressure for 60minutes

A uniform thin film 60 nm thick was formed by the spin coating.

Next, the pyridine derivative (HB-1) was deposited as a hole blockinglayer 9 to a thickness of 5 nm. The vacuum deposition was conducted at acrucible temperature of 237° C. to 238° C., a deposition rate of 0.1 nmper second, and a degree of vacuum of 9.3 to 9.2×10⁻⁵ Pa (about 7.0 to6.9×10⁻⁶ Torr).

Next, the aluminum 8-hydroxyquinoline complex (ET-1) was deposited as anelectron transport layer 8 in the same manner. The temperature of thecrucible for the aluminum 8-hydroxyquinoline complex in this procedurewas controlled within the range of from 294° C. to 288° C. The vacuumdeposition was conducted at a degree of vacuum of 9.1 to 8.5×10⁻⁵ Pa(about 6.8 to 6.4×10⁻⁶ Torr) and a deposition rate of 0.11 to 0.12 nmper second to yield a film 30 nm thick.

The temperature of the substrate upon vacuum deposition of the holeblocking layer 9 and the electron transport layer 8 was kept to roomtemperature.

The device which had been subjected to vacuum deposition up to theelectron transport layer 8 was once taken out of the vacuum depositionapparatus into the atmosphere. A 2-mm width striped shadow mask as amask for vacuum deposition of a cathode was brought into intimatecontact with the device perpendicularly to the ITO stripe of the anode2, and the device was placed in another vacuum deposition apparatus. Theapparatus was evacuated to a degree of vacuum of 2.0×10⁻⁶ Torr (about2.6×10⁻⁴ Pa) or less in the same manner as with the organic layers.

As an electron injection layer 5, lithium fluoride (LiF) was depositedto a thickness of 0.5 nm on the electron transport layer 8. The vacuumdeposition was conducted at a deposition rate of 0.02 nm per second anda degree of vacuum of 2.0×10⁻⁶ Torr (about 2.6×10⁻⁴ Pa) using amolybdenum boat.

Next, aluminum was heated in the same manner using a molybdenum boat andwas deposited at a deposition rate of 0.2 nm per second and a degree ofvacuum of 3.2×10⁻⁶ Torr (about 4.2×10⁻⁴ Pa) to yield an aluminum layer80 nm thick. A cathode 6 was thus completed.

The temperature of the substrate upon vacuum deposition of thetwo-layered cathode 6 was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. The maximal wavelength inemission spectrum of the device was 519 nm, which was identified asbeing from the iridium complex (D2). The chromaticity in terms of CIE(x, y) was (0.365, 0.591).

Example 9 Device Preparation 9

An organic electroluminescent device having the structure shown in FIG.7 was prepared in the following manner.

After conducting film-formation up to the hole injection layer 3 in thesame manner as with Example 5, an organic light emitting layer 4 wasformed by wet coating in the following manner. A composition for anorganic electroluminescent device was prepared by dissolving thefollowing compounds (T8) and (D2) as materials for a light emittinglayer 4 in concentrations in a solvent mentioned below. The compositionwas applied by spin coating under the following conditions, to therebyyield the organic light emitting layer 4.

<Conditions of Spin Coating>

Solvent: xylene

Concentrations in coating composition: 2.0 percent by weight of T8

-   -   0.1 percent by weight of D2

Revolution number of spinner: 1500 rpm

Revolution time of spinner: 30 seconds

Drying condition: drying at 130° C. under reduced pressure for 60minutes

A uniform thin film 60 nm thick was formed by the spin coating.

Next, the pyridine derivative (HB-1) was deposited as a hole blockinglayer 9 to a thickness of 5.1 nm. The vacuum deposition was conducted ata crucible temperature of 273° C., a deposition rate of 0.1 nm persecond, and a degree of vacuum of 3.3×10⁻⁴ Pa (about 2.5×10⁻⁶ Torr).

Next, the aluminum 8-hydroxyquinoline complex (ET-1) was deposited as anelectron transport layer 8 in the same manner. The temperature of thecrucible for the aluminum 8-hydroxyquinoline complex in this procedurewas controlled within the range of from 376° C. to 371° C. The vacuumdeposition was conducted at a degree of vacuum of 3.1×10⁻⁴ Pa (about2.3×10⁻⁶ Torr) and a deposition rate of 0.11 to 0.12 nm per second toyield a film 30 nm thick.

The temperature of the substrate upon vacuum deposition of the holeblocking layer 9 and the electron transport layer 8 was kept to roomtemperature.

The device which had been subjected to vacuum deposition up to theelectron transport layer 8 was once taken out of the vacuum depositionapparatus into the atmosphere. A 2-mm width striped shadow mask as amask for vacuum deposition of a cathode was brought into intimatecontact with the device perpendicularly to the ITO stripe of the anode2, and the device was placed in another vacuum deposition apparatus. Theapparatus was evacuated to a degree of vacuum of 2.5×10⁻⁶ Torr (about3.3×10⁻⁴ Pa) or less in the same manner as with the organic layers.

As an electron injection layer 5, lithium fluoride (LiF) was depositedto a thickness of 0.5 nm on the electron transport layer 8. The vacuumdeposition was conducted at a deposition rate of 0.006 nm per second anda degree of vacuum of 2.6×10⁻⁶ Torr (about 3.5×10⁻⁴ Pa).

Next, aluminum was heated in the same manner using a molybdenum boat andwas deposited at a deposition rate of 0.1 to 0.35 nm per second and adegree of vacuum of 3.4 to 4.5×10⁻⁶ Torr (about 4.5 to 6.0×10⁻⁴ Pa) toyield an aluminum layer 80 nm thick. A cathode 6 was thus completed.

The temperature of the substrate upon vacuum deposition of thetwo-layered cathode 6 was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. The maximal wavelength inemission spectrum of the device was 513 nm, which was identified asbeing from the iridium complex (D2). The chromaticity in terms of CIE(x, y) was (0.311, 0.622).

Example 10 Device Preparation 10

An organic electroluminescent device having the structure shown in FIG.7 was prepared in the following manner.

An anode 2 was formed on a glass substrate 1, and rinsing was conductedin the same manner as with Example 4. Thereafter, a hole injection layer3 was formed by wet coating in the following manner. As materials forthe hole injection layer 3, a polymeric compound (PB-3) having aweight-average molecular weight of 29400 and a number-average molecularweight of 12600 and containing an aromatic amino group of the followingstructural formula, and an electron-acceptor (A-2) of the followingstructural formula were applied by spin coating under the followingconditions.

<Conditions of Spin Coating>

Solvent: ethyl benzoate

Concentrations in coating composition: 2.0 percent by weight of PB-3

-   -   0.8 percent by weight of A-2

Revolution number of spinner: 1500 rpm

Revolution time of spinner: 30 seconds

Drying condition: drying at 230° C. for 3 hours

A uniform thin film 30 nm thick was formed by the spin coating.

Subsequently, an organic light emitting layer 4 was formed by wetcoating in the following manner. A composition for an organicelectroluminescent device was prepared by dissolving the followingcompounds (T6), (T9) and (D2) in concentrations in a solvent mentionedbelow. The composition was applied by spin coating under the followingconditions, to thereby yield the organic light emitting layer 4.

The term “Ink Storage” in the following conditions for spin coatingrefers to the condition and time period of storage of the compositionfor an organic electroluminescent device between its preparation and usein spin coating.

<Conditions of Spin Coating>

Ink storage: storage at 4° C. in a dark place for 18 days

Solvent: toluene

Concentrations in coating composition: 1.0 percent by weight of T6

-   -   1.0 percent by weight of T9    -   0.1 percent by weight of D2

Revolution number of spinner: 1500 rpm

Revolution time of spinner: 30 seconds

Drying condition: drying at 80° C. under reduced pressure for 60 minutes

A uniform thin film 60 nm thick was formed by the spin coating.

Next, the pyridine derivative (HB-1) was deposited as a hole blockinglayer 9 to a thickness of 5.1 nm. The vacuum deposition was conducted ata crucible temperature of 307° C. to 312° C., a deposition rate of 0.07to 0.13 nm per second, and a degree of vacuum of 2.7×10⁻⁴ Pa (about2.0×10⁻⁶ Torr).

Next, the aluminum 8-hydroxyquinoline complex (ET-1) was deposited as anelectron transport layer 8 on the hole blocking layer 9 in the samemanner. The temperature of the crucible for the aluminum8-hydroxyquinoline complex in this procedure was controlled within therange of from 469° C. to 444° C. The vacuum deposition was conducted ata degree of vacuum of 6.0 to 3.3×10⁻⁴ Pa (about 4.5 to 2.5×10⁻⁶ Torr)and a deposition rate of 0.07 to 0.13 nm per second to yield a film 30nm thick.

The temperature of the substrate upon vacuum deposition of the holeblocking layer 9 and the electron transport layer 8 was kept to roomtemperature.

The device which had been subjected to vacuum deposition up to theelectron transport layer 8 was once taken out of the vacuum depositionapparatus into the atmosphere. A 2-mm width striped shadow mask as amask for vacuum deposition of a cathode was brought into intimatecontact with the device perpendicularly to the ITO stripe of the anode2, and the device was placed in another vacuum deposition apparatus. Theapparatus was evacuated to a degree of vacuum of 1.5×10⁻⁶ Torr (about3.0×10⁻⁴ Pa) or less in the same manner as with the organic layers.

As an electron injection layer 5, lithium fluoride (LiF) was depositedto a thickness of 0.5 nm on the electron transport layer 8. The vacuumdeposition was conducted at a deposition rate of 0.007 to 0.01 nm persecond and a degree of vacuum of 2.2 to 2.3×10⁻⁶ Torr (about 2.9 to3.0×10⁻⁴ Pa).

Next, aluminum was heated in the same manner using a molybdenum boat andwas deposited at a deposition rate of 0.08 to 0.35 nm per second and adegree of vacuum of 3.8 to 6.5×10⁻⁶ Torr (about 5.1 to 8.7×10⁻⁴ Pa) toyield an aluminum layer 80 nm thick. A cathode 6 was thus completed.

The temperature of the substrate upon vacuum deposition of thetwo-layered cathode 6 was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. The maximal wavelength inemission spectrum of the device was 512 nm, which was identified asbeing from the iridium complex (D2). The chromaticity in terms of CIE(x, y) was (0.309, 0.619).

Example 11 Device Preparation 11

An organic electroluminescent device having the structure shown in FIG.7 was prepared in the same manner as with Example 10, except forcarrying out the ink storage in “Conditions of spin coating” at atemperature of 20° C. in the formation of the organic light emittinglayer 4.

The maximal wavelength in emission spectrum of the device was 513 nm,which was identified as being from the iridium complex (D2). Thechromaticity in terms of CIE (x, y) was (0.314, 0.617).

Example 12 Device Preparation 12

An organic electroluminescent device having the structure shown in FIG.7 was prepared in the following manner.

Film-formation up to the organic light emitting layer 4 was conducted inthe same manner as with Example 10, except for carrying out the inkstorage for a time period of 7 days before spin coating in the formationof the light emitting layer 4. Thereafter, the pyridine derivative(HB-1) was deposited as a hole blocking layer 9 to a thickness of 5 nm.The vacuum deposition was conducted at a crucible temperature of 327° C.to 332° C., a deposition rate of 0.08 nm per second, and a degree ofvacuum of 1.7×10⁻⁴ Pa (about 1.3×10⁻⁶ Torr).

Next, the aluminum 8-hydroxyquinoline complex (ET-1) was deposited as anelectron transport layer 8 on the hole blocking layer 9 in the samemanner. The temperature of the crucible for the aluminum8-hydroxyquinoline complex in this procedure was controlled within therange of from 440° C. to 425° C. The vacuum deposition was conducted ata degree of vacuum of 1.7 to 1.6×10⁻⁴ Pa (about 1.3 to 1.2×10⁻⁶ Torr)and a deposition rate of 0.1 to 0.14 nm per second to yield a film 30 nmthick.

The temperature of the substrate upon vacuum deposition of the holeblocking layer 9 and the electron transport layer 8 was kept to roomtemperature.

The device which had been subjected to vacuum deposition up to theelectron transport layer 8 was once taken out of the vacuum depositionapparatus into the atmosphere. A 2-mm width striped shadow mask as amask for vacuum deposition of a cathode was brought into intimatecontact with the device perpendicularly to the ITO stripe of the anode2, and the device was placed in another vacuum deposition apparatus. Theapparatus was evacuated to a degree of vacuum of 1.5×10⁻⁶ Torr (about1.96×10⁻⁴ Pa) or less in the same manner as with the organic layers.

As an electron injection layer 5, lithium fluoride (LiF) was depositedto a thickness of 0.5 nm on the electron transport layer 8. The vacuumdeposition was conducted at a deposition rate of 0.008 to 0.013 nm persecond and a degree of vacuum of 1.5 to 1.6×10⁻⁶ Torr (about 2.0 to2.1×10⁻⁴ Pa) using a molybdenum boat.

Next, aluminum was heated in the same manner using a molybdenum boat andwas deposited at a deposition rate of 0.05 to 0.42 nm per second and adegree of vacuum of 2.5 to 7.0×10⁻⁶ Torr (about 3.3 to 9.3×10⁻⁴ Pa) toyield an aluminum layer 80 nm thick. A cathode 6 was thus completed.

The temperature of the substrate upon vacuum deposition of thetwo-layered cathode 6 was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. The maximal wavelength inemission spectrum of the device was 513 nm, which was identified asbeing from the iridium complex (D2). The chromaticity in terms of CIE(x, y) was (0.315, 0.617).

Example 13 Device Preparation 13

An organic electroluminescent device having the structure shown in FIG.7 was prepared in the same manner as with Example 12, except forcarrying out the ink storage at a temperature of 20° C. before spincoating in the formation of the organic light emitting layer 4.

The maximal wavelength in emission spectrum of the device was 513 nm,which was identified as being from the iridium complex (D2). Thechromaticity in terms of CIE (x, y) was (0.314, 0.617).

Example 14 Device Preparation 14

An organic electroluminescent device having the structure shown in FIG.7 was prepared in the following manner.

Film-formation up to the organic light emitting layer 4 was conducted inthe same manner as with Example 10, except for using the ink(composition) in spin coating immediately after its preparation withoutstorage in the formation of the light emitting layer 4. Thereafter, thepyridine derivative (HB-1) was deposited as a hole blocking layer 9 to athickness of 5.1 nm. The vacuum deposition was conducted at a crucibletemperature of 315° C. to 319° C., a deposition rate of 0.07 to 0.094 nmper second, and a degree of vacuum of 3.1 to 2.7×10⁻⁴ Pa (about 2.3 to2.0×10⁻⁶ Torr).

Next, the aluminum 8-hydroxyquinoline complex (ET-1) was deposited as anelectron transport layer 8 on the hole blocking layer 9 in the samemanner. The temperature of the crucible for the aluminum8-hydroxyquinoline complex in this procedure was controlled within therange of from 481° C. to 391° C. The vacuum deposition was conducted ata degree of vacuum of 2.7 to 3.6×10⁻⁴ Pa (about 2.0 to 2.7×10⁻⁶ Torr)and a deposition rate of 0.11 to 0.18 nm per second to yield a film 30nm thick.

The temperature of the substrate upon vacuum deposition of the holeblocking layer 9 and the electron transport layer 8 was kept to roomtemperature.

The device which had been subjected to vacuum deposition up to theelectron transport layer 8 was once taken out of the vacuum depositionapparatus into the atmosphere. A 2-mm width striped shadow mask as amask for vacuum deposition of a cathode was brought into intimatecontact with the device perpendicularly to the ITO stripe of the anode2, and the device was placed in another vacuum deposition apparatus. Theapparatus was evacuated to a degree of vacuum of 3.1×10⁻⁶ Torr (about4.1×10⁻⁴ Pa) or less in the same manner as with the organic layers.

As an electron injection layer 5, lithium fluoride (LiF) was depositedto a thickness of 0.5 nm on the electron transport layer 8. The vacuumdeposition was conducted at a deposition rate of 0.007 to 0.012 nm persecond and a degree of vacuum of 3.2 to 3.3×10⁻⁶ Torr (about 4.3 to4.4×10⁻⁴ Pa) using a molybdenum boat. Next, aluminum was heated in thesame manner using a molybdenum boat and was deposited at a depositionrate of 0.05 to 0.47 nm per second and a degree of vacuum of 4.0 to7.4×10⁻⁶ Torr (about 5.3 to 9.8×10⁻⁴ Pa) to yield an aluminum layer 80nm thick. A cathode 6 was thus completed.

The temperature of the substrate upon vacuum deposition of thetwo-layered cathode 6 was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. The maximal wavelength inemission spectrum of the device was 512 nm, which was identified asbeing from the iridium complex (D2). The chromaticity in terms of CIE(x, y) was (0.303, 0.622).

Example 15 Device Preparation 15

An organic electroluminescent device having the structure shown in FIG.7 was prepared in the following manner.

Film-formation up to the hole injection layer 3 was conducted in thesame manner as with Example 10, except that the concentration of thecompound (A-2) was 0.4 percent by weight and drying was carried out at230° C. for 15 minutes in the spin coating in the formation of the holeinjection layer 3. Thereafter, an organic light emitting layer 4 wasformed by wet coating in the following manner. A composition for anorganic electroluminescent device was prepared by dissolving thefollowing compounds (T6), (T12) and (D4) as materials for the lightemitting layer 4 in concentrations in a solvent mentioned below. Thecomposition was applied by spin coating under the following conditions,to thereby yield the organic light emitting layer 4.

<Conditions of Spin Coating>

Solvent: toluene

Concentrations in coating composition: 1.0 percent by weight of T6

-   -   1.0 percent by weight of T12    -   0.1 percent by weight of D4

Revolution number of spinner: 1500 rpm

Revolution time of spinner: 30 seconds

Drying condition: drying at 80° C. under reduced pressure for 60 minutes

A uniform thin film 60 nm thick was formed by the spin coating.

Next, the pyridine derivative (HB-1) was deposited as a hole blockinglayer 9 to a thickness of 5 nm. The vacuum deposition was conducted at acrucible temperature of 238° C. to 249° C., a deposition rate of 0.014to 0.024 nm per second, and a degree of vacuum of 3.5 to 3.7×10⁻⁴ Pa(about 2.6 to 2.8×10⁻⁶ Torr).

Next, the aluminum 8-hydroxyquinoline complex (ET-1) was deposited as anelectron transport layer 8 on the hole blocking layer 9 in the samemanner. The temperature of the crucible for the aluminum8-hydroxyquinoline complex in this procedure was controlled within therange of from 240° C. to 247° C. The vacuum deposition was conducted ata degree of vacuum of 3.7 to 3.3×10⁻⁴ Pa (about 2.8 to 2.5×10⁻⁶ Torr)and a deposition rate of 0.1 to 0.11 nm per second to yield a film 30 nmthick.

The temperature of the substrate upon vacuum deposition of the holeblocking layer 9 and the electron transport layer 8 was kept to roomtemperature.

The device which had been subjected to vacuum deposition up to theelectron transport layer 8 was once taken out of the vacuum depositionapparatus into the atmosphere. A 2-mm width striped shadow mask as amask for vacuum deposition of a cathode was brought into intimatecontact with the device perpendicularly to the ITO stripe of the anode2, and the device was placed in another vacuum deposition apparatus. Theapparatus was evacuated to a degree of vacuum of 2.1×10⁻⁶ Torr (about2.2×10⁻⁴ Pa) or less in the same manner as with the organic layers.

As an electron injection layer 5, lithium fluoride (LiF) was depositedto a thickness of 0.5 nm on the electron transport layer 8. The vacuumdeposition was conducted at a deposition rate of 0.006 to 0.008 nm persecond and a degree of vacuum of 2.3 to 2.4×10⁻⁶ Torr (about 3.1 to3.2×10⁻⁴ Pa) using a molybdenum boat.

Next, aluminum was heated in the same manner using a molybdenum boat andwas deposited at a deposition rate of 0.25 to 0.41 nm per second and adegree of vacuum of 2.5 to 7.4×10⁻⁶ Torr (about 3.3 to 9.8×10⁻⁴ Pa) toyield an aluminum layer 80 nm thick. A cathode 6 was thus completed.

The temperature of the substrate upon vacuum deposition of thetwo-layered cathode 6 was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. A peak of 474 nm was observedin emission spectrum of the device, which was identified as being fromthe iridium complex (D4).

Comparative Example 1

An organic electroluminescent device having the structure shown in FIG.6 was prepared in the following manner.

Film-formation up to the hole injection layer 3 was conducted in thesame manner as with Example 10, except that the concentration of thecompound (A-2) was 0.4 percent by weight in spin coating in theformation of the hole injection layer 3. Thereafter, an organic lightemitting layer 4 was formed by wet coating in the following manner. Asmaterials for the light emitting layer 4, the following compounds (T10),(T11) and (D3) were dissolved in concentrations in a solvent mentionedbelow to yield a composition for an organic electroluminescent device.The composition was applied by spin coating under the followingconditions, to thereby yield the organic light emitting layer 4.

<Conditions of Spin Coating>

Solvent: chloroform

Concentrations in coating composition: 1.0 percent by weight of T10

-   -   1.0 percent by weight of T11    -   0.1 percent by weight of D3

Revolution number of spinner: 1500 rpm

Revolution time of spinner: 30 seconds

Drying condition: drying at 80° C. under reduced pressure for 60 minutes

A uniform thin film 100 nm thick was formed by the spin coating.

Next, the following compound (ET-2) was deposited as an electrontransport layer 8. The vacuum deposition herein was conducted at adegree of vacuum of 1.79 to 1.71×10⁻⁴ Pa (about 1.3×10⁻⁶ Torr) and adeposition rate of 0.09 to 0.1 nm per second, to thereby yield a film 20nm thick.

Next, as an electron injection layer 5, lithium fluoride (LiF) wasdeposited to a thickness of 0.5 nm on the electron transport layer 8.The vacuum deposition was conducted at a deposition rate of 0.009 to0.013 nm per second and a degree of vacuum of 1.3×10⁻⁶ Torr (about1.76×10⁻⁴ Pa) using a molybdenum boat.

Next, aluminum was heated in the same manner using a molybdenum boat andwas deposited at a deposition rate of 0.06 to 0.19 nm per second and adegree of vacuum of 2.1×10⁻⁶ Torr (about 3.15 to 10.0×10⁻⁴ Pa) to yieldan aluminum layer 80 nm thick. A cathode 6 was thus completed.

The temperature of the substrate upon vapor deposition of these layerswas kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. The maximal wavelength inemission spectrum of the device was 514 nm, which was identified asbeing from the iridium complex (D3). The chromaticity in terms of CIE(x, y) was (0.308, 0.621).

The oxidation/reduction potentials of host materials and dopantmaterials used in the formation of the organic light emitting layer 4 inExamples 4 to 15 and Comparative Example 1 are shown in Table 3.

The normalized luminance half-lives and initial luminance when driven ata constant current, and the current efficiencies and drive voltages uponlight emission at a luminance of 100 cd/m² are shown in Table 4.

TABLE 3 Oxidation Potential Reduction Potential (V vs. SCE) (V vs. SCE)T5 1.20 −2.02 T6 1.30 −2.09 T7 1.24 −1.95 T8 1.34 −1.99 T9 0.89 −2.56T10 1.27 −2.40 T11 0.78 −2.41 T12 0.94 −2.48 D2 0.64 −2.44 D3 0.65 −2.48D4 1.29 −1.88

TABLE 4 Life Initial Current Drive Normalized Converted Lumi- Effi-Volt- Host Dopant Luminance at 1000 nance ciency age Material MaterialHalf-life cd/m2 * (cd/m2) (cd/A) (V) T5 D2  2.70  9.7 2500 22.4 6.0 T5D2  5.41 19.5 2500 26.4 6.3 T6 D2 10.81 38.9 2500 — — T6 D3 20.27 16.4 857 16.7 7.2 T7 D2 21.62  8.4  508 — — T8 D2 10.81 10.8 1000 11.0 9.1T6/T9 D2  3.78  3.8 1000 19.3 8.6 T6/T9 D2  3.78  3.8 1000 19.7 9.0T6/T9 D2  4.05  4.1 1000 15.1 8.3 T6/T9 D2  4.05  4.1 1000 15.7 8.8T6/T9 D2  1.62  1.6 1000 21.9 7.2 T10/T11 D3  1.00  1.0 1000  9.1 7.2 *Data with initial luminance other than 1000 cd/m² are converted with anaccelerating factor of the 1.4th power of the luminance. This is definedas the “Life converted at 1000 cd/m²”

Of the data in Table 4, Table 5 shows the current efficiencies and drivevoltages of devices, and the normalized luminance half-lives and initialluminance of the devices when compositions for organicelectroluminescent devices were stored at 4° C. or 20° C. in theatmosphere (air) in a dark place.

TABLE 5 Normal- Storage Condition Current Drive ized Initial Temper-Effi- Volt- Lumi- Lumi- ature Time ciency age nance nance (° C.) (day)(cd/A) (V) Half-life (cd/m²) Example10  4 18 19.3 8.6 2.5 1000 Example1120 18 19.7 9.0 2.5 1000 Example12  4  7 15.1 8.3 2.33 1000 Example13 20 7 15.7 8.8 2.33 1000 Example14 —  0 21.9 7.2 1 1000

These results demonstrate that compositions for organicelectroluminescent devices according to the present invention have longpot lives, and devices prepared using the compositions have highluminous efficiencies and long lives.

Referential Example 1

An organic electroluminescent device was prepared in the followingmanner, in which a light emitting layer was formed by vapor deposition.The resulting organic electroluminescent device has a layer structure aswith the organic electroluminescent device shown in FIG. 7, except forhaving a hole transport layer instead of the hole injection layer 3.

An indium-tin oxide (ITO) transparent electroconductive film depositedto a thickness of 150 nm on a glass substrate 1 (sputtered film; sheetresistance: 15Ω) was patterned in a 2-mm width striped pattern using acommon photolithography technique and etching with hydrochloric acid,thereby forming an anode 2. The patterned ITO substrate was rinsed bysequentially carrying out ultrasonic cleaning in acetone, rinsing withpure water, and ultrasonic cleaning in isopropyl alcohol, followed bydrying in a nitrogen blow and UV/ozone cleaning.

Next, a hole injection layer 3 was formed by wet coating in thefollowing manner. As materials for the hole injection layer 3, apolymeric compound (PB-2) having a weight-average molecular weight of29400 and a number-average molecular weight of 12600 and containing anaromatic amino group of the following structural formula, and anelectron-acceptor (A-2) of the following structural formula were appliedby spin coating under the following conditions.

<Conditions of Spin Coating>

Solvent: ethyl benzoate

Concentrations in coating composition: 2.0 percent by weight of PB-2

-   -   0.4 percent by weight of A-2

Revolution number of spinner: 1500 rpm

Revolution time of spinner: 30 seconds

Drying condition: drying at 230° C. for 15 minutes

A uniform thin film 30 nm thick was formed by the spin coating.

Subsequently, the following amine derivative (T11) was deposited as ahole transport layer at a crucible temperature of 254° C. to 274° C. anda deposition rate of 0.09 to 0.13 nm per second to a thickness of 40 nm.The vacuum deposition was conducted at a degree of vacuum of 5.2 to5.3×10⁻⁵ Pa (about 3.9 to 4.0×10⁻⁷ Torr).

Next, the following compound (T10) together with an iridium complex (D5)of the following structural formula was deposited as an organic lightemitting layer 4 by vacuum deposition. The vacuum deposition was carriedout at a crucible temperature of 288° C. to 293° C. and a depositionrate of 0.08 to 0.09 nm per second for the compound (T10), and at acrucible temperature of 247° C. to 248° C. and a deposition rate of0.005 nm per second for the compound (D5), to thereby yield a film 30 nmthick. The vacuum deposition was conducted at a degree of vacuum of 5.4to 5.5×10⁻⁵ Pa (about 4.1×10⁻⁷ Torr). The compound (D5) has an oxidationpotential of +0.71 V and a reduction potential of −2.3 V.

Next, the pyridine derivative (HB-1) was deposited as a hole blockinglayer 9 to a thickness of 5 nm. The vacuum deposition was conducted at acrucible temperature of 230° C. to 233° C., a deposition rate of 0.09 to0.11 nm per second, and a degree of vacuum of 5.3 to 5.1×10⁻⁵ Pa (about4.0 to 3.8×10⁻⁷ Torr).

Next, the aluminum 8-hydroxyquinoline complex (ET-1) was deposited as anelectron transport layer 8 on the hole blocking layer 9 in the samemanner. The temperature of the crucible for the aluminum8-hydroxyquinoline complex in this procedure was controlled within therange of from 263° C. to 259° C. The vacuum deposition was conducted ata degree of vacuum of 5.3 to 5.2×10⁻⁵ Pa (about 4.0 to 3.9×10⁻⁶ Torr)and a deposition rate of 0.1 to 0.13 nm per second to yield a film 30 nmthick.

The temperature of the substrate upon vacuum deposition of the holeblocking layer 9 and the electron transport layer 8 was kept to roomtemperature.

The device which had been subjected to vacuum deposition up to theelectron transport layer 8 was once taken out of the vacuum depositionapparatus into the atmosphere. A 2-mm width striped shadow mask as amask for vacuum deposition of a cathode was brought into intimatecontact with the device perpendicularly to the ITO stripe of the anode2, and the device was placed in another vacuum deposition apparatus. Theapparatus was evacuated to a degree of vacuum of 1.4×10⁻⁶ Torr (about1.9×10⁻⁴ Pa) or less in the same manner as with the organic layers.

As an electron injection layer 5, lithium fluoride (LiF) was depositedto a thickness of 0.5 nm on the electron transport layer 8. The vacuumdeposition was conducted at a deposition rate of 0.6 nm per second and adegree of vacuum of 2.2×10⁻⁶ Torr (about 2.9×10⁻⁴ Pa) using a molybdenumboat. Next, aluminum was heated in the same manner using a molybdenumboat and was deposited at a deposition rate of 0.1 to 0.5 nm per secondand a degree of vacuum of 4.8 to 10.0×10⁻⁶ Torr (about 6.4 to 13.3×10⁻⁴Pa) to yield an aluminum layer 80 nm thick. A cathode 6 was thuscompleted.

The temperature of the substrate upon vacuum deposition of thetwo-layered cathode 6 was kept to room temperature.

Thus, an organic electroluminescent device having a light-emitting areaof 2 mm wide and 2 mm long was prepared. The maximal wavelength inemission spectrum of the device was 512 nm, which was identified asbeing from the iridium complex (D5). The chromaticity in terms of CIE(x, y) was (0.294, 0.588).

Referential Example 2

An organic electroluminescent device was prepared in the same manner aswith Referential Example 1, except for forming an organic light emittinglayer 4 by vacuum deposition under the following conditions using thefollowing compound (T5) and an iridium complex (D5) of the followingstructural formula.

The vacuum deposition was conducted at a crucible temperature of 428° C.to 425° C. and a deposition rate of 0.09 to 0.08 nm per second for thecompound (T5), and at a crucible temperature of 251° C. to 254° C. and adeposition rate of 0.005 nm per second for the compound (D5), to yield afilm 30 nm thick. The vacuum deposition was conducted at a degree ofvacuum of 6.0 to 6.1×10⁻⁵ Pa (about 4.5 to 4.6×10⁻⁷ Torr).

The maximal wavelength in emission spectrum of the device was 513 nm,which was identified as being from the iridium complex (D5). Thechromaticity in terms of CIE (x, y) was (0.301, 0.597).

Table 6 shows, of the devices produced by vacuum deposition, the currentefficiencies and drive voltages at a luminance of 100 cd/m², and thenormalized luminance half-lives when driven at a constant currentprovided that the initial luminance is 2500 cd/m².

TABLE 6 Current Drive Normalized Initial Efficiency Voltage LuminanceLuminance (cd/A) (V) Half-life (cd/m²) Referential Example 1 28.8 5.0 12500 Referential Example 2 22.4 6.1 0.64 2500

The results in Table 6 demonstrate that there is not so much differencebetween effects of the devices prepared according to vacuum deposition,regardless of whether or not the condition as specified in the presentinvention is satisfied.

While the present invention has been shown and described in detail withreference to specific embodiments thereof, it will be understood bythose skilled in the art that various changes and modifications may bemade without departing from the spirit and scope of the presentinvention.

The present application is based on Japanese Patent Application No.2005-044250 filed on Feb. 21, 2005, the entire contents of which beingincorporated herein by reference.

1. A composition for an organic electroluminescent device, comprising aphosphorescent material, a charge transport material, and a solvent,wherein each of the phosphorescent material and the charge transportmaterial is independently an unpolymerized organic compound, and whereinthe first oxidation potential of the phosphorescent material ED⁺, thefirst reduction potential of the phosphorescent material ED⁻, the firstoxidation potential of the charge transport material ET⁺, and the firstreduction potential of the charge transport material ET⁻ satisfy thefollowing condition:E _(T) ⁻+0.1≦E _(D) ⁻ <E _(T) ⁺ ≦E _(D) ⁺−0.1  (1)orE _(D) ⁻+0.1≦E _(T) ⁻ <E _(D) ⁺ ≦E _(T) ⁺−0.1  (2).
 2. The compositionfor an organic electroluminescent device according to claim 1, whereinsaid condition E_(D) ⁻+0.1≦E_(T) ⁻<E_(D) ⁺≦E_(T) ⁺−0.1 is satisfied, andan absolute value of the difference between E_(D) ⁺ and E_(T) ⁺|E_(D)⁺−E_(T) ⁺| is 0.1 V or more.
 3. The composition for an organicelectroluminescent device according to claim 1, wherein said conditionE_(D) ⁻+0.1≦E_(T) ⁻<E_(D) ⁺≦E_(T) ⁺−0.1 is satisfied, an absolute valueof the difference between E_(D) ⁺ and E_(T) ⁻ |E_(D) ⁺−E_(T) ⁻| is 1.0 Vor more.
 4. The composition for an organic electroluminescent deviceaccording to claim 1, wherein said condition E_(D) ⁻+0.1≦E_(T) ⁻<E_(D)⁺≦E_(T) ⁺−0.1 is satisfied, an absolute value of the difference betweenE_(D) ⁻ and E_(T) ⁻ |E_(D) ⁻−E_(T) ⁻| is 0.10 V or more.
 5. Thecomposition for an organic electroluminescent device according to claim1, wherein said condition E_(D) ⁻+0.1≦E_(T) ⁻<E_(D) ⁺≦E_(T) ⁺−0.1 issatisfied, an absolute value of the difference between E_(T) ⁺ and E_(D)⁻ |E_(T) ⁺−E_(D) ⁻| is 1.5 V or more.
 6. The composition for an organicelectroluminescent device according to claim 1, wherein the conditionE_(T) ⁻+0.1≦E_(D) ⁻<E_(T) ⁺≦E_(D) ⁺−0.1 is satisfied, and an absolutevalue of the difference between E_(D) ⁻ and E_(T) ⁻ |E_(D) ⁻−E_(T) ⁻| is0.1 V or more.
 7. The composition for an organic electroluminescentdevice according to claim 1, wherein the condition E_(T) ⁻+0.1≦E_(D)⁻<E_(T) ⁺≦E_(D) ⁺−0.1 is satisfied, and an absolute value of thedifference between E_(T) ⁺ and E_(D) ⁻ |E_(T) ⁺−E_(D) ⁻| is 1.0 V ormore.
 8. The composition for an organic electroluminescent deviceaccording to claim 1, wherein the condition E_(T) ⁻+0.1≦E_(D) ⁻<E_(T)⁺≦E_(D) ⁺−0.1 is satisfied, and an absolute value of the differencebetween E_(D) ⁺ and E_(T) ⁺ |E_(D) ⁺−E_(T) ⁺| is 0.1 V or more.
 9. Thecomposition for an organic electroluminescent device according to claim1, wherein the condition E_(T) ⁻+0.1≦E_(D) ⁻<E_(T) ⁺≦E_(D) ⁺−0.1 issatisfied, and an absolute value of the difference between E_(T) ⁻ andE_(D) ⁺ |E_(T) ⁻−E_(D) ⁺| is 1.5 V or more.
 10. A thin film for anorganic electroluminescent device formed from the composition for anorganic electroluminescent device of claim 1 by a wet coating process.11. The thin film for an organic electroluminescent device according toclaim 10, wherein the thin film has a refractive index of 1.78 or lesswith respect to light having a wavelength of 500 nm to 600 nm.
 12. Atransfer member for a thin film for an organic electroluminescentdevice, comprising a base material and a thin film arranged on the basematerial, wherein the thin film is formed from the composition for anorganic electroluminescent device of claim 1 by a wet coating process.13. An organic electroluminescent device comprising a substrate bearingan anode, a cathode, and an organic light emitting layer arrangedbetween the two electrodes, wherein the organic light emitting layer isa layer formed by using the transfer member for a thin film for anorganic electroluminescent device of claim
 12. 14. An organicelectroluminescent device comprising a substrate bearing an anode, acathode, and an organic light emitting layer arranged between the anodeand cathode, wherein the organic light emitting layer is a layer formedfrom the composition for an organic electroluminescent device of claim 1by a wet coating process.
 15. The organic electroluminescent deviceaccording to claim 13, further comprising a hole injection layer betweenthe organic light emitting layer and the anode.
 16. The organicelectroluminescent device according to claim 14, further comprising ahole injection layer between the organic light emitting layer and theanode.
 17. The organic electroluminescent device according to claim 13,further comprising an electron injection layer between the organic lightemitting layer and the cathode.
 18. The organic electroluminescentdevice according to claim 14, further comprising an electron injectionlayer between the organic light emitting layer and the cathode.